TECHNICAL FIELD 
       [0001]    This disclosure relates to personal active noise reduction (ANR) devices to reduce acoustic noise in the vicinity of at least one of a user&#39;s ears. 
       BACKGROUND 
       [0002]    Headphones and other physical configurations of personal ANR device worn about the ears of a user for purposes of isolating the user&#39;s ears from unwanted environmental sounds have become commonplace. In particular, ANR headphones in which unwanted environmental noise sounds are countered with the active generation of anti-noise sounds, have become highly prevalent, even in comparison to headphones or ear plugs employing only passive noise reduction (PNR) technology, in which a user&#39;s ears are simply physically isolated from environmental noises. Especially of interest to users are ANR headphones that also incorporate audio listening functionality, thereby enabling a user to listen to electronically provided audio (e.g., playback of recorded audio or audio received from another device) without the intrusion of unwanted environmental noise sounds. 
         [0003]    Unfortunately, despite various improvements made over time, existing personal ANR devices continue to suffer from a variety of drawbacks. Foremost among those drawbacks are undesirably high rates of power consumption leading to short battery life, undesirably narrow ranges of audible frequencies in which unwanted environmental noise sounds are countered through ANR, instances of unpleasant ANR-originated sounds, and instances of actually creating more unwanted noise sounds than whatever unwanted environmental sounds may be reduced. 
       SUMMARY 
       [0004]    At initialization of an ANR circuit (i.e., at so-called boot time), attempts are made to alternately obtain ANR settings from an external storage device by operating the ANR circuit as a master of a bus and from an external processing device by operating the ANR circuit as a slave of the bus. Such alternating attempts may be repeated until the ANR settings are loaded. 
         [0005]    In one aspect, a method of loading ANR settings includes placing an ANR circuit coupled to a bus in a master mode on the bus; causing the ANR circuit to attempt to retrieve the ANR settings from an external storage device through the bus; in response to the attempt to retrieve the ANR settings from an external storage device through the bus being successful, loading the ANR settings into a storage device incorporated into the ANR circuit and placing the ANR circuit in a slave mode on the bus to enable the ANR circuit to accept data from an external processing device through the bus; in response to the attempt to retrieve the ANR settings from an external storage device through the bus not being successful, placing the ANR circuit in a slave mode on the bus to enable the ANR circuit to accept the ANR settings from an external processing device through the bus and awaiting receipt of the ANR settings from an external processing device through the bus for a selected period of time; and in response to the attempt to retrieve the ANR settings from an external storage device through the bus not being successful and in response to the ANR settings being received from an external processing device through the bus during the selected period of time, loading the ANR settings into the storage device incorporated into the ANR circuit and placing the ANR circuit in a slave mode on the bus to enable the ANR circuit to accept data from an external processing device through the bus. 
         [0006]    Implementations may include, and are not limited to, one or more of the following features. The method may further include in response to the attempt to retrieve the ANR settings from an external storage device through the bus not being successful; and in response to the ANR settings not being received from an external processing device through the bus during the selected period of time: placing the ANR circuit in a master mode on the bus, again; causing the ANR circuit to again attempt to retrieve the ANR settings from an external storage device through the bus; in response to the attempt to retrieve the ANR settings again from an external storage device through the bus being successful, loading the ANR settings into the storage device incorporated into the ANR circuit and placing the ANR circuit in a slave mode on the bus, again, to enable the ANR circuit to accept data from an external processing device through the bus; and in response to the attempt to retrieve the ANR settings again from an external storage device through the bus not being successful, placing the ANR circuit in a slave mode on the bus, again, to enable the ANR circuit to accept the ANR settings from an external processing device through the bus and awaiting receipt of the ANR settings from an external processing device through the bus for the selected period of time. 
         [0007]    The method may further include configuring a dynamically configurable portion of the ANR circuit to adopt a signal processing topology specified by the ANR settings that define at least one pathway for the flow of digital data associated with at least one of a feedback-based ANR function, a feedforward-based ANR function and a pass-through audio function; configuring at least one digital filter of the ANR circuit with at least one coefficient taken from the ANR settings; and/or loading other ANR settings received from an external processing device into the storage device incorporated into the ANR circuit and configuring the dynamically configurable portion of the ANR circuit to adopt another signal processing topology specified by the other ANR settings. 
         [0008]    In one aspect, an apparatus includes a processing device incorporated into the ANR circuit; an interface coupling the ANR circuit to a bus; and a storage device incorporated into the ANR circuit storing a sequence of instructions. When the sequence of instructions is executed by the processing device, the processing device is caused the processing device to: operate the interface to place the ANR in a master mode on the bus and to attempt to retrieve ANR settings from an external storage device through the bus; in response to the attempt to retrieve the ANR settings from an external storage device through the bus being successful, load the ANR settings into the storage device incorporated into the ANR circuit and operate the interface to place the ANR circuit in a slave mode on the bus to enable the ANR circuit to accept data from an external processing device through the bus; in response to the attempt to retrieve the ANR settings from an external storage device through the bus not being successful, operate the interface to place the ANR circuit in a slave mode on the bus to enable the ANR circuit to accept the ANR settings from an external processing device through the bus and await receipt of the ANR settings from an external processing device through the bus for a selected period of time; and in response to the attempt to retrieve the ANR settings from an external storage device through the bus not being successful and in response to the ANR settings being received from an external processing device through the bus during the selected period of time, load the ANR settings into the storage device incorporated into the ANR circuit and operate the interface to place the ANR circuit in a slave mode on the bus to enable the ANR circuit to accept data from an external processing device through the bus. 
         [0009]    Implementations may include, and are not limited to, one or more of the following features. In response to the attempt to retrieve the ANR settings from an external storage device through the bus not being successful and in response to the ANR settings not being received from an external processing device through the bus during the selected period of time, the processing device may be further caused to: operate the interface to place the ANR circuit in a master mode on the bus, again, and to again attempt to retrieve the ANR settings from an external storage device through the bus; in response to the attempt to retrieve the ANR settings again from an external storage device through the bus being successful, load the ANR settings into the storage device incorporated into the ANR circuit and operate the interface to place the ANR circuit in a slave mode on the bus, again, to enable the ANR circuit to accept data from an external processing device through the bus; and in response to the attempt to retrieve the ANR settings again from an external storage device through the bus not being successful, operate the interface to place the ANR circuit in a slave mode on the bus, again, to enable the ANR circuit to accept the ANR settings from an external processing device through the bus and await receipt of the ANR settings from an external processing device through the bus for the selected period of time. 
         [0010]    The ANR circuit may further include a dynamically configurable portion, wherein following the loading of the ANR settings into the storage device incorporated into the ANR circuit, the processing device is further caused to configure the dynamically configurable portion to adopt a signal processing topology specified by the ANR settings that defines at least one pathway for the flow of digital data associated with at least one of a feedback-based ANR function, a feedforward-based ANR function and a pass-through audio function; and following the loading of the ANR settings into the storage device incorporated into the ANR circuit and in response to receiving other ANR settings from an external processing device through the bus, the processing device may be further caused to load the other ANR settings into the storage device incorporated into the ANR circuit and configure the dynamically configurable portion of the ANR circuit to adopt another signal processing topology specified by the other ANR settings. The ANR circuit may further include a digital filter, wherein following the loading of the ANR settings into the storage device incorporated into the ANR circuit, the processing device is further caused to configure the digital filter with at least one coefficient taken from the ANR settings; and following the loading of the ANR settings into the storage device incorporated into the ANR circuit and in response to receiving other ANR settings from an external processing device through the bus, the processing device is further caused to load the other ANR settings into the storage device incorporated into the ANR circuit and configure the digital filter with at least one coefficient taken from the other ANR settings. 
         [0011]    Other features and advantages of the invention will be apparent from the description and claims that follow. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a block diagram of portions of an implementation of a personal ANR device. 
           [0013]      FIGS. 2   a  through  2   f  depict possible physical configurations of the personal ANR device of  FIG. 1 . 
           [0014]      FIGS. 3   a  and  3   b  depict possible internal architectures of an ANR circuit of the personal ANR device of  FIG. 1 . 
           [0015]      FIGS. 4   a  through  4   g  depict possible signal processing topologies that may be adopted by the ANR circuit of the personal ANR device of  FIG. 1 . 
           [0016]      FIGS. 5   a  through  5   e  depict possible filter block topologies that may be adopted by the ANR circuit of the personal ANR device of  FIG. 1 . 
           [0017]      FIGS. 6   a  through  6   c  depict possible variants of triple-buffering that may be adopted by the ANR circuit of the personal ANR device of  FIG. 1 . 
           [0018]      FIG. 7   a  depicts a possible additional portion of the internal architecture of  FIG. 3   a.    
           [0019]      FIG. 7   b  depicts a possible additional portion of the internal architecture of  FIG. 3   b.    
           [0020]      FIG. 8  is a flowchart of a possible boot loading sequence that may be adopted by the ANR circuit of the personal ANR device of  FIG. 1 . 
           [0021]      FIG. 9   a  depicts a possible internal architecture of an ADC of the ANR circuit of the personal ANR device of  FIG. 1 . 
           [0022]      FIG. 9   b  depicts a possible additional portion of any of the signal processing topologies of  FIGS. 4   a  through  4   g.    
           [0023]      FIGS. 10   a  and  10   b  depict possible additional portions of any of the signal processing topologies of  FIGS. 4   a  through  4   g.    
       
    
    
     DETAILED DESCRIPTION 
       [0024]    What is disclosed and what is claimed herein is intended to be applicable to a wide variety of personal ANR devices, i.e., devices that are structured to be at least partly worn by a user in the vicinity of at least one of the user&#39;s ears to provide ANR functionality for at least that one ear. It should be noted that although various specific implementations of personal ANR devices, such as headphones, two-way communications headsets, earphones, earbuds, wireless headsets (also known as “earsets”) and ear protectors are presented with some degree of detail, such presentations of specific implementations are intended to facilitate understanding through the use of examples, and should not be taken as limiting either the scope of disclosure or the scope of claim coverage. 
         [0025]    It is intended that what is disclosed and what is claimed herein is applicable to personal ANR devices that provide two-way audio communications, one-way audio communications (i.e., acoustic output of audio electronically provided by another device), or no communications, at all. It is intended that what is disclosed and what is claimed herein is applicable to personal ANR devices that are wirelessly connected to other devices, that are connected to other devices through electrically and/or optically conductive cabling, or that are not connected to any other device, at all. It is intended that what is disclosed and what is claimed herein is applicable to personal ANR devices having physical configurations structured to be worn in the vicinity of either one or both ears of a user, including and not limited to, headphones with either one or two earpieces, over-the-head headphones, behind-the-neck headphones, headsets with communications microphones (e.g., boom microphones), wireless headsets (i.e., earsets), single earphones or pairs of earphones, as well as hats or helmets incorporating one or two earpieces to enable audio communications and/or ear protection. Still other physical configurations of personal ANR devices to which what is disclosed and what is claimed herein are applicable will be apparent to those skilled in the art. 
         [0026]    Beyond personal ANR devices, what is disclosed and claimed herein is also meant to be applicable to the provision of ANR in relatively small spaces in which a person may sit or stand, including and not limited to, phone booths, car passenger cabins, etc. 
         [0027]      FIG. 1  provides a block diagram of a personal ANR device  1000  structured to be worn by a user to provide active noise reduction (ANR) in the vicinity of at least one of the user&#39;s ears. As will also be explained in greater detail, the personal ANR device  1000  may have any of a number of physical configurations, some possible ones of which are depicted in  FIGS. 2   a  through  2   f.  Some of these depicted physical configurations incorporate a single earpiece  100  to provide ANR to only one of the user&#39;s ears, and others incorporate a pair of earpieces  100  to provide ANR to both of the user&#39;s ears. However, it should be noted that for the sake of simplicity of discussion, only a single earpiece  100  is depicted and described in relation to  FIG. 1 . As will also be explained in greater detail, the personal ANR device  1000  incorporates at least one ANR circuit  2000  that may provide either or both of feedback-based ANR and feedforward-based ANR, in addition to possibly further providing pass-through audio.  FIGS. 3   a  and  3   b  depict a couple of possible internal architectures of the ANR circuit  2000  that are at least partly dynamically configurable. Further,  FIGS. 4   a  through  4   e  depict some possible signal processing topologies and  FIGS. 5   a  through  5   e  depict some possible filter block topologies that may the ANR circuit  2000  may be dynamically configured to adopt. Further, the provision of either or both of feedback-based ANR and feedforward-based ANR is in addition to at least some degree of passive noise reduction (PNR) provided by the structure of each earpiece  100 . Still further,  FIGS. 6   a  through  6   c  depict various forms of triple-buffering that may be employed in dynamically configuring signal processing topologies, filter block topologies and/or still other ANR settings. 
         [0028]    Each earpiece  100  incorporates a casing  110  having a cavity  112  at least partly defined by the casing  110  and by at least a portion of an acoustic driver  190  disposed within the casing to acoustically output sounds to a user&#39;s ear. This manner of positioning the acoustic driver  190  also partly defines another cavity  119  within the casing  110  that is separated from the cavity  112  by the acoustic driver  190 . The casing  110  carries an ear coupling  115  surrounding an opening to the cavity  112  and having a passage  117  that is formed through the ear coupling  115  and that communicates with the opening to the cavity  112 . In some implementations, an acoustically transparent screen, grill or other form of perforated panel (not shown) may be positioned in or near the passage  117  in a manner that obscures the cavity and/or the passage  117  from view for aesthetic reasons and/or to protect components within the casing  110  from damage. At times when the earpiece  100  is worn by a user in the vicinity of one of the user&#39;s ears, the passage  117  acoustically couples the cavity  112  to the ear canal of that ear, while the ear coupling  115  engages portions of the ear to form at least some degree of acoustic seal therebetween. This acoustic seal enables the casing  110 , the ear coupling  115  and portions of the user&#39;s head surrounding the ear canal (including portions of the ear) to cooperate to acoustically isolate the cavity  112 , the passage  117  and the ear canal from the environment external to the casing  110  and the user&#39;s head to at least some degree, thereby providing some degree of PNR. 
         [0029]    In some variations, the cavity  119  may be coupled to the environment external to the casing  110  via one or more acoustic ports (only one of which is shown), each tuned by their dimensions to a selected range of audible frequencies to enhance characteristics of the acoustic output of sounds by the acoustic driver  190  in a manner readily recognizable to those skilled in the art. Also, in some variations, one or more tuned ports (not shown) may couple the cavities  112  and  119 , and/or may couple the cavity  112  to the environment external to the casing  110 . Although not specifically depicted, screens, grills or other forms of perforated or fibrous structures may be positioned within one or more of such ports to prevent passage of debris or other contaminants therethrough and/or to provide a selected degree of acoustic resistance therethrough. 
         [0030]    In implementations providing feedforward-based ANR, a feedforward microphone  130  is disposed on the exterior of the casing  110  (or on some other portion of the personal ANR device  1000 ) in a manner that is acoustically accessible to the environment external to the casing  110 . This external positioning of the feedforward microphone  130  enables the feedforward microphone  130  to detect environmental noise sounds, such as those emitted by an acoustic noise source  9900 , in the environment external to the casing  110  without the effects of any form of PNR or ANR provided by the personal ANR device  1000 . As those familiar with feedforward-based ANR will readily recognize, these sounds detected by the feedforward microphone  130  are used as a reference from which feedforward anti-noise sounds are derived and then acoustically output into the cavity  112  by the acoustic driver  190 . The derivation of the feedforward anti-noise sounds takes into account the characteristics of the PNR provided by the personal ANR device  1000 , characteristics and position of the acoustic driver  190  relative to the feedforward microphone  130 , and/or acoustic characteristics of the cavity  112  and/or the passage  117 . The feedforward anti-noise sounds are acoustically output by the acoustic driver  190  with amplitudes and time shifts calculated to acoustically interact with the noise sounds of the acoustic noise source  9900  that are able to enter into the cavity  112 , the passage  117  and/or an ear canal in a subtractive manner that at least attenuates them. 
         [0031]    In implementations providing feedback-based ANR, a feedback microphone  120  is disposed within the cavity  112 . The feedback microphone  120  is positioned in close proximity to the opening of the cavity  112  and/or the passage  117  so as to be positioned close to the entrance of an ear canal when the earpiece  100  is worn by a user. The sounds detected by the feedback microphone  120  are used as a reference from which feedback anti-noise sounds are derived and then acoustically output into the cavity  112  by the acoustic driver  190 . The derivation of the feedback anti-noise sounds takes into account the characteristics and position of the acoustic driver  190  relative to the feedback microphone  120 , and/or the acoustic characteristics of the cavity  112  and/or the passage  117 , as well as considerations that enhance stability in the provision of feedback-based ANR. The feedback anti-noise sounds are acoustically output by the acoustic driver  190  with amplitudes and time shifts calculated to acoustically interact with noise sounds of the acoustic noise source  9900  that are able to enter into the cavity  112 , the passage  117  and/or the ear canal (and that have not been attenuated by whatever PNR) in a subtractive manner that at least attenuates them. 
         [0032]    The personal ANR device  1000  further incorporates one of the ANR circuit  2000  associated with each earpiece  100  of the personal ANR device  1000  such that there is a one-to-one correspondence of ANR circuits  2000  to earpieces  100 . Either a portion of or substantially all of each ANR circuit  2000  may be disposed within the casing  110  of its associated earpiece  100 . Alternatively and/or additionally, a portion of or substantially all of each ANR circuit  2000  may be disposed within another portion of the personal ANR device  1000 . Depending on whether one or both of feedback-based ANR and feedforward-based ANR are provided in an earpiece  100  associated with the ANR circuit  2000 , the ANR circuit  2000  is coupled to one or both of the feedback microphone  120  and the feedforward microphone  130 , respectively. The ANR circuit  2000  is further coupled to the acoustic driver  190  to cause the acoustic output of anti-noise sounds. 
         [0033]    In some implementations providing pass-through audio, the ANR circuit  2000  is also coupled to an audio source  9400  to receive pass-through audio from the audio source  9400  to be acoustically output by the acoustic driver  190 . The pass-through audio, unlike the noise sounds emitted by the acoustic noise source  9900 , is audio that a user of the personal ANR device  1000  desires to hear. Indeed, the user may wear the personal ANR device  1000  to be able to hear the pass-through audio without the intrusion of the acoustic noise sounds. The pass-through audio may be a playback of recorded audio, transmitted audio, or any of a variety of other forms of audio that the user desires to hear. In some implementations, the audio source  9400  may be incorporated into the personal ANR device  1000 , including and not limited to, an integrated audio playback component or an integrated audio receiver component. In other implementations, the personal ANR device  1000  incorporates a capability to be coupled either wirelessly or via an electrically or optically conductive cable to the audio source  9400  where the audio source  9400  is an entirely separate device from the personal ANR device  1000  (e.g., a CD player, a digital audio file player, a cell phone, etc.). 
         [0034]    In other implementations pass-through audio is received from a communications microphone  140  integrated into variants of the personal ANR device  1000  employed in two-way communications in which the communications microphone  140  is positioned to detect speech sounds produced by the user of the personal ANR device  1000 . In such implementations, an attenuated or otherwise modified form of the speech sounds produced by the user may be acoustically output to one or both ears of the user as a communications sidetone to enable the user to hear their own voice in a manner substantially similar to how they normally would hear their own voice when not wearing the personal ANR device  1000 . 
         [0035]    In support of the operation of at least the ANR circuit  2000 , the personal ANR device  1000  may further incorporate one or both of a storage device  170 , a power source  180  and/or a processing device (not shown). As will be explained in greater detail, the ANR circuit  2000  may access the storage device  170  (perhaps through a digital serial interface) to obtain ANR settings with which to configure feedback-based and/or feedforward-based ANR. As will also be explained in greater detail, the power source  180  may be a power storage device of limited capacity (e.g., a battery). 
         [0036]      FIGS. 2   a  through  2   f  depict various possible physical configurations that may be adopted by the personal ANR device  1000  of  FIG. 1 . As previously discussed, different implementations of the personal ANR device  1000  may have either one or two earpieces  100 , and are structured to be worn on or near a user&#39;s head in a manner that enables each earpiece  100  to be positioned in the vicinity of a user&#39;s ear. 
         [0037]      FIG. 2   a  depicts an “over-the-head” physical configuration  1500   a  of the personal ANR device  1000  that incorporates a pair of earpieces  100  that are each in the form of an earcup, and that are connected by a headband  102 . However, and although not specifically depicted, an alternate variant of the physical configuration  1500   a  may incorporate only one of the earpieces  100  connected to the headband  102 . Another alternate variant of the physical configuration  1500   a  may replace the headband  102  with a different band structured to be worn around the back of the head and/or the back of the neck of a user. 
         [0038]    In the physical configuration  1500   a,  each of the earpieces  100  may be either an “on-ear” (also commonly called “supra-aural”) or an “around-ear” (also commonly called “circum-aural”) form of earcup, depending on their size relative to the pinna of a typical human ear. As previously discussed, each earpiece  100  has the casing  110  in which the cavity  112  is formed, and that  110  carries the ear coupling  115 . In this physical configuration, the ear coupling  115  is in the form of a flexible cushion (possibly ring-shaped) that surrounds the periphery of the opening into the cavity  112  and that has the passage  117  formed therethrough that communicates with the cavity  112 . 
         [0039]    Where the earpieces  100  are structured to be worn as over-the-ear earcups, the casing  110  and the ear coupling  115  cooperate to substantially surround the pinna of an ear of a user. Thus, when such a variant of the personal ANR device  1000  is correctly worn, the headband  102  and the casing  110  cooperate to press the ear coupling  115  against portions of a side of the user&#39;s head surrounding the pinna of an ear such that the pinna is substantially hidden from view. Where the earpieces  100  are structured to be worn as on-ear earcups, the casing  110  and ear coupling  115  cooperate to overlie peripheral portions of a pinna that surround the entrance of an associated ear canal. Thus, when correctly worn, the headband  102  and the casing  110  cooperate to press the ear coupling  115  against portions of the pinna in a manner that likely leaves portions of the periphery of the pinna visible. The pressing of the flexible material of the ear coupling  115  against either portions of a pinna or portions of a side of a head surrounding a pinna serves both to acoustically couple the ear canal with the cavity  112  through the passage  117 , and to form the previously discussed acoustic seal to enable the provision of PNR. 
         [0040]      FIG. 2   b  depicts another over-the-head physical configuration  1500   b  that is substantially similar to the physical configuration  1500   a,  but in which one of the earpieces  100  additionally incorporates a communications microphone  140  connected to the casing  110  via a microphone boom  142 . When this particular one of the earpieces  100  is correctly worn, the microphone boom  142  extends from the casing  110  and generally alongside a portion of a cheek of a user to position the communications microphone  140  closer to the mouth of the user to detect speech sounds acoustically output from the user&#39;s mouth. However, and although not specifically depicted, an alternative variant of the physical configuration  1500   b  is possible in which the communications microphone  140  is more directly disposed on the casing  110 , and the microphone boom  142  is a hollow tube that opens on one end in the vicinity of the user&#39;s mouth and on the other end in the vicinity of the communications microphone  140  to convey sounds from the vicinity of the user&#39;s mouth to the vicinity of the communications microphone  140 . 
         [0041]      FIG. 2   b  also depicts the other of the earpieces  100  with broken lines to make clear that still another variant of the physical configuration  1500   b  of the personal ANR device  1000  is possible that incorporates only the one of the earpieces  100  that incorporates the microphone boom  142  and the communications microphone  140 . In such another variant, the headband  102  would still be present and would continue to be worn over the head of the user. 
         [0042]      FIG. 2   c  depicts an “in-ear” (also commonly called “intra-aural”) physical configuration  1500   c  of the personal ANR device  1000  that incorporates a pair of earpieces  100  that are each in the form of an in-ear earphone, and that may or may not be connected by a cord and/or by electrically or optically conductive cabling (not shown). However, and although not specifically depicted, an alternate variant of the physical configuration  1500   c  may incorporate only one of the earpieces  100 . 
         [0043]    As previously discussed, each of the earpieces  100  has the casing  110  in which the open cavity  112  is formed, and that carries the ear coupling  115 . In this physical configuration, the ear coupling  115  is in the form of a substantially hollow tube-like shape defining the passage  117  that communicates with the cavity  112 . In some implementations, the ear coupling  115  is formed of a material distinct from the casing  110  (possibly a material that is more flexible than that from which the casing  110  is formed), and in other implementations, the ear coupling  115  is formed integrally with the casing  110 . 
         [0044]    Portions of the casing  110  and/or of the ear coupling  115  cooperate to engage portions of the concha and/or the ear canal of a user&#39;s ear to enable the casing  110  to rest in the vicinity of the entrance of the ear canal in an orientation that acoustically couples the cavity  112  with the ear canal through the ear coupling  115 . Thus, when the earpiece  100  is properly positioned, the entrance to the ear canal is substantially “plugged” to create the previously discussed acoustic seal to enable the provision of PNR. 
         [0045]      FIG. 2   d  depicts another in-ear physical configuration  1500   d  of the personal ANR device  1000  that is substantially similar to the physical configuration  1500   c,  but in which one of the earpieces  100  is in the form of a single-ear headset (sometimes also called an “earset”) that additionally incorporates a communications microphone  140  disposed on the casing  110 . When this earpiece  100  is correctly worn, the communications microphone  140  is generally oriented towards the vicinity of the mouth of the user in a manner chosen to detect speech sounds produced by the user. However, and although not specifically depicted, an alternative variant of the physical configuration  1500   d  is possible in which sounds from the vicinity of the user&#39;s mouth are conveyed to the communications microphone  140  through a tube (not shown), or in which the communications microphone  140  is disposed on a boom (not shown) connected to the casing  110  and positioning the communications microphone  140  in the vicinity of the user&#39;s mouth. 
         [0046]    Although not specifically depicted in  FIG. 2   d,  the depicted earpiece  100  of the physical configuration  1500   d  having the communications microphone  140  may or may not be accompanied by another earpiece having the form of an in-ear earphone (such as one of the earpieces  100  depicted in  FIG. 2   c ) that may or may not be connected to the earpiece  100  depicted in  FIG. 2   d  via a cord or conductive cabling (also not shown). 
         [0047]      FIG. 2   e  depicts a two-way communications handset physical configuration  1500   e  of the personal ANR device  1000  that incorporates a single earpiece  100  that is integrally formed with the rest of the handset such that the casing  110  is the casing of the handset, and that may or may not be connected by conductive cabling (not shown) to a cradle base with which it may be paired. In a manner not unlike one of the earpieces  100  of an on-the-ear variant of either of the physical configurations  1500   a  and  1500   b,  the earpiece  100  of the physical configuration  1500   e  carries a form of the ear coupling  115  that is configured to be pressed against portions of the pinna of an ear to enable the passage  117  to acoustically couple the cavity  112  to an ear canal. In various possible implementations, ear coupling  115  may be formed of a material distinct from the casing  110 , or may be formed integrally with the casing  110 . 
         [0048]      FIG. 2   f  depicts another two-way communications handset physical configuration  1500   f  of the personal ANR device  1000  that is substantially similar to the physical configuration  1500   e,  but in which the casing  110  is shaped somewhat more appropriately for portable wireless communications use, possibly incorporating user interface controls and/or display(s) to enable the dialing of phone numbers and/or the selection of radio frequency channels without the use of a cradle base. 
         [0049]      FIGS. 3   a  and  3   b  depict possible internal architectures, either of which may be employed by the ANR circuit  2000  in implementations of the personal ANR device  1000  in which the ANR circuit  2000  is at least partially made up of dynamically configurable digital circuitry. In other words, the internal architectures of  FIGS. 3   a  and  3   b  are dynamically configurable to adopt any of a wide variety of signal processing topologies and filter block topologies during operation of the ANR circuit  2000 .  FIGS. 4   a - g  depict various examples of signal processing topologies that may be adopted by the ANR circuit  2000  in this manner, and  FIGS. 5   a - e  depict various examples of filter block topologies that may also be adopted by the ANR circuit  2000  for use within an adopted signal processing topology in this manner. However, and as those skilled in the art will readily recognize, other implementations of the personal ANR device  1000  are possible in which the ANR circuit  2000  is largely or entirely implemented with analog circuitry and/or digital circuitry lacking such dynamic configurability. 
         [0050]    In implementations in which the circuitry of the ANR circuit  2000  is at least partially digital, analog signals representing sounds that are received or output by the ANR circuit  2000  may require conversion into or creation from digital data that also represents those sounds. More specifically, in both of the internal architectures  2200   a  and  2200   b,  analog signals received from the feedback microphone  120  and the feedforward microphone  130 , as well as whatever analog signal representing pass-through audio may be received from either the audio source  9400  or the communications microphone  140 , are digitized by analog-to-digital converters (ADCs) of the ANR circuit  2000 . Also, whatever analog signal is provided to the acoustic driver  190  to cause the acoustic driver  190  to acoustically output anti-noise sounds and/or pass-through audio is created from digital data by a digital-to-analog converter (DAC) of the ANR circuit  2000 . Further, either analog signals or digital data representing sounds may be manipulated to alter the amplitudes of those represented sounds by either analog or digital forms, respectively, of variable gain amplifiers (VGAs). 
         [0051]      FIG. 3   a  depicts a possible internal architecture  2200   a  of the ANR circuit  2000  in which digital circuits that manipulate digital data representing sounds are selectively interconnected through one or more arrays of switching devices that enable those interconnections to be dynamically configured during operation of the ANR circuit  2000 . Such a use of switching devices enables pathways for movement of digital data among various digital circuits to be defined through programming. More specifically, blocks of digital filters of varying quantities and/or types are able to be defined through which digital data associated with feedback-based ANR, feedforward-based ANR and pass-through audio are routed to perform these functions. In employing the internal architecture  2200   a,  the ANR circuit  2000  incorporates ADCs  210 ,  310  and  410 ; a processing device  510 ; a storage  520 ; an interface (I/F)  530 ; a switch array  540 ; a filter bank  550 ; and a DAC  910 . Various possible variations may further incorporate one or more of analog VGAs  125 ,  135  and  145 ; a VGA bank  560 ; a clock bank  570 ; a compression controller  950 ; a further ADC  955 ; and/or an audio amplifier  960 . 
         [0052]    The ADC  210  receives an analog signal from the feedback microphone  120 , the ADC  310  receives an analog signal from the feedforward microphone  130 , and the ADC  410  receives an analog signal from either the audio source  9400  or the communications microphone  140 . As will be explained in greater detail, one or more of the ADCs  210 ,  310  and  410  may receive their associated analog signals through one or more of the analog VGAs  125 ,  135  and  145 , respectively. The digital outputs of each of the ADCs  210 ,  310  and  410  are coupled to the switch array  540 . Each of the ADCs  210 ,  310  and  410  may be designed to employ a variant of the widely known sigma-delta analog-to-digital conversion algorithm for reasons of power conservation and inherent ability to reduce digital data representing audible noise sounds that might otherwise be introduced as a result of the conversion process. However, as those skilled in the art will readily recognize, any of a variety of other analog-to-digital conversion algorithms may be employed. Further, in some implementations, at least the ADC  410  may be bypassed and/or entirely dispensed with where at least the pass-through audio is provided to the ANR circuit  2000  as digital data, rather than as an analog signal. 
         [0053]    The filter bank  550  incorporates multiple digital filters, each of which has its inputs and outputs coupled to the switch array  540 . In some implementations, all of the digital filters within the filter bank  550  are of the same type, while in other implementations, the filter bank  550  incorporates a mixture of different types of digital filters. As depicted, the filter bank  550  incorporates a mixture of multiple downsampling filters  552 , multiple biquadratic (biquad) filters  554 , multiple interpolating filters  556 , and multiple finite impulse response (FIR) filters  558 , although other varieties of filters may be incorporated, as those skilled in the art will readily recognize. Further, among each of the different types of digital filters may be digital filters optimized to support different data transfer rates. By way of example, differing ones of the biquad filters  554  may employ coefficient values of differing bit-widths, or differing ones of the FIR filters  558  may have differing quantities of taps. The VGA bank  560  (if present) incorporates multiple digital VGAs, each of which has its inputs and outputs coupled to the switch array  540 . Also, the DAC  910  has its digital input coupled to the switch array  540 . The clock bank  570  (if present) provides multiple clock signal outputs coupled to the switch array  540  that simultaneously provide multiple clock signals for clocking data between components at selected data transfer rates and/or other purposes. In some implementations, at least a subset of the multiple clock signals are synchronized multiples of one another to simultaneously support different data transfer rates in different pathways in which the movement of data at those different data transfer rates in those different pathways is synchronized. 
         [0054]    The switching devices of the switch array  540  are operable to selectively couple different ones of the digital outputs of the ADCs  210 ,  310  and  410 ; the inputs and outputs of the digital filters of the filter bank  550 ; the inputs and outputs of the digital VGAs of the VGA bank  560 ; and the digital input of the DAC  910  to form a set of interconnections therebetween that define a topology of pathways for the movement of digital data representing various sounds. The switching devices of the switch array  540  may also be operable to selectively couple different ones of the clock signal outputs of the clock bank  570  to different ones of the digital filters of the filter bank  550  and/or different ones of the digital VGAs of the VGA bank  560 . It is largely in this way that the digital circuitry of the internal architecture  2200   a  is made dynamically configurable. In this way, varying quantities and types of digital filters and/or digital VGAs may be positioned at various points along different pathways defined for flows of digital data associated with feedback-based ANR, feedforward-based ANR and pass-through audio to modify sounds represented by the digital data and/or to derive new digital data representing new sounds in each of those pathways. Also, in this way, different data transfer rates may be selected by which digital data is clocked at different rates in each of the pathways. 
         [0055]    In support of feedback-based ANR, feedforward-based ANR and/or pass-through audio, the coupling of the inputs and outputs of the digital filters within the filter bank  550  to the switch array  540  enables inputs and outputs of multiple digital filters to be coupled through the switch array  540  to create blocks of filters. As those skilled in the art will readily recognize, by combining multiple lower-order digital filters into a block of filters, multiple lower-order digital filters may be caused to cooperate to implement higher order functions without the use of a higher-order filter. Further, in implementations having a variety of types of digital filters, blocks of filters may be created that employ a mix of filters to perform a still greater variety of functions. By way of example, with the depicted variety of filters within the filter bank  550 , a filter block (i.e., a block of filters) may be created having at least one of the downsampling filters  552 , multiple ones of the biquad filters  554 , at least one of the interpolating filters  556 , and at least one of the FIR filters  558 . 
         [0056]    In some implementations, at least some of the switching devices of the switch array  540  may be implemented with binary logic devices enabling the switch array  540 , itself, to be used to implement basic binary math operations to create summing nodes where pathways along which different pieces of digital data flow are brought together in a manner in which those different pieces of digital data are arithmetically summed, averaged, and/or otherwise combined. In such implementations, the switch array  540  may be based on a variant of dynamically programmable array of logic devices. Alternatively and/or additionally, a bank of binary logic devices or other form of arithmetic logic circuitry (not shown) may also be incorporated into the ANR circuit  2000  with the inputs and outputs of those binary logic devices and/or other form of arithmetic logic circuitry also being coupled to the switch array  540 . 
         [0057]    In the operation of switching devices of the switch array  540  to adopt a topology by creating pathways for the flow of data representing sounds, priority may be given to creating a pathway for the flow of digital data associated with feedback-based ANR that has as low a latency as possible through the switching devices. Also, priority may be given in selecting digital filters and VGAs that have as low a latency as possible from among those available in the filter bank  550  and the VGA bank  560 , respectively. Further, coefficients and/or other settings provided to digital filters of the filter bank  550  that are employed in the pathway for digital data associated with feedback-based ANR may be adjusted in response to whatever latencies are incurred from the switching devices of the switch array  540  employed in defining the pathway. Such measures may be taken in recognition of the higher sensitivity of feedback-based ANR to the latencies of components employed in performing the function of deriving and/or acoustically outputting feedback anti-noise sounds. Although such latencies are also of concern in feedforward-based ANR, feedforward-based ANR is generally less sensitive to such latencies than feedback-based ANR. As a result, a degree of priority less than that given to feedback-based ANR, but greater than that given to pass-through audio, may be given to selecting digital filters and VGAs, and to creating a pathway for the flow of digital data associated with feedforward-based ANR. 
         [0058]    The processing device  510  is coupled to the switch array  540 , as well as to both the storage  520  and the interface  530 . The processing device  510  may be any of a variety of types of processing device, including and not limited to, a general purpose central processing unit (CPU), a digital signal processor (DSP), a reduced instruction set computer (RISC) processor, a microcontroller, or a sequencer. The storage  520  may be based on any of a variety of data storage technologies, including and not limited to, dynamic random access memory (DRAM), static random access memory (SRAM), ferromagnetic disc storage, optical disc storage, or any of a variety of nonvolatile solid state storage technologies. Indeed, the storage  520  may incorporate both volatile and nonvolatile portions. Further, it will be recognized by those skilled in the art that although the storage  520  is depicted and discussed as if it were a single component, the storage  520  may be made up of multiple components, possibly including a combination of volatile and nonvolatile components. The interface  530  may support the coupling of the ANR circuit  2000  to one or more digital communications buses, including digital serial buses by which the storage device  170  (not to be confused with the storage  520 ) and/or other devices external to the ANR circuit  2000  (e.g., other processing devices, or other ANR circuits) may be coupled. Further, the interface  530  may provide one or more general purpose input/output (GPIO) electrical connections and/or analog electrical connections to support the coupling of manually-operable controls, indicator lights or other devices, such as a portion of the power source  180  providing an indication of available power. 
         [0059]    In some implementations, the processing device  510  accesses the storage  520  to read a sequence of instructions of a loading routine  522 , that when executed by the processing device  510 , causes the processing device  510  to operate the interface  530  to access the storage device  170  to retrieve one or both of the ANR routine  525  and the ANR settings  527 , and to store them in the storage  520 . In other implementations, one or both of the ANR routine  525  and the ANR settings  527  are stored in a nonvolatile portion of the storage  520  such that they need not be retrieved from the storage device  170 , even if power to the ANR circuit  2000  is lost. 
         [0060]    Regardless of whether one or both of the ANR routine  525  and the ANR settings  527  are retrieved from the storage device  170 , or not, the processing device  510  accesses the storage  520  to read a sequence of instructions of the ANR routine  525 . The processing device  510  then executes that sequence of instructions, causing the processing device  510  to configure the switching devices of the switch array  540  to adopt a topology defining pathways for flows of digital data representing sounds and/or to provide differing clock signals to one or more digital filters and/or VGAs, as previously detailed. In some implementations, the processing device  510  is caused to configure the switching devices in a manner specified by a portion of the ANR settings  527 , which the processing device  510  is also caused to read from the storage  520 . Further, the processing device  510  is caused to set filter coefficients of various digital filters of the filter bank  550 , gain settings of various VGAs of the VGA bank  560 , and/or clock frequencies of the clock signal outputs of the clock bank  570  in a manner specified by a portion of the ANR settings  527 . 
         [0061]    In some implementations, the ANR settings  527  specify multiple sets of filter coefficients, gain settings, clock frequencies and/or configurations of the switching devices of the switch array  540 , of which different sets are used in response to different situations. In other implementations, execution of sequences of instructions of the ANR routine  525  causes the processing device  510  to derive different sets of filter coefficients, gain settings, clock frequencies and/or switching device configurations in response to different situations. By way of example, the processing device  510  may be caused to operate the interface  530  to monitor a signal from the power source  180  that is indicative of the power available from the power source  180 , and to dynamically switch between different sets of filter coefficients, gain settings, clock frequencies and/or switching device configurations in response to changes in the amount of available power. 
         [0062]    By way of another example, the processing device  510  may be caused to monitor characteristics of sounds represented by digital data involved in feedback-based ANR, feedforward-based ANR and/or pass-through audio to determine whether or not it is desirable to alter the degree feedback-based and/or feedforward-based ANR provided. As will be familiar to those skilled in the art, while providing a high degree of ANR can be very desirable where there is considerable environmental noise to be attenuated, there can be other situations where the provision of a high degree of ANR can actually create a noisier or otherwise more unpleasant acoustic environment for a user of a personal ANR device than would the provision of less ANR. Therefore, the processing device  510  may be caused to alter the provision of ANR to adjust the degree of attenuation and/or the range of frequencies of environmental noise attenuated by the ANR provided in response to observed characteristics of one or more sounds. Further, as will also be familiar to those skilled in the art, where a reduction in the degree of attenuation and/or the range of frequencies is desired, it may be possible to simplify the quantity and/or type of filters used in implementing feedback-based and/or feedforward-based ANR, and the processing device  510  may be caused to dynamically switch between different sets of filter coefficients, gain settings, clock frequencies and/or switching device configurations to perform such simplifying, with the added benefit of a reduction in power consumption. 
         [0063]    The DAC  910  is provided with digital data from the switch array  540  representing sounds to be acoustically output to an ear of a user of the personal ANR device  1000 , and converts it to an analog signal representing those sounds. The audio amplifier  960  receives this analog signal from the DAC  910 , and amplifies it sufficiently to drive the acoustic driver  190  to effect the acoustic output of those sounds. 
         [0064]    The compression controller  950  (if present) monitors the sounds to be acoustically output for an indication of their amplitude being too high, indications of impending instances of clipping, actual instances of clipping, and/or other impending or actual instances of other audio artifacts. The compression controller  150  may either directly monitor digital data provided to the DAC  910  or the analog signal output by the audio amplifier  960  (through the ADC  955 , if present). In response to such an indication, the compression controller  950  may alter gain settings of one or more of the analog VGAs  125 ,  135  and  145  (if present); and/or one or more of the VGAs of the VGA bank  560  placed in a pathway associated with one or more of the feedback-based ANR, feedforward-based ANR and pass-through audio functions to adjust amplitude, as will be explained in greater detail. Further, in some implementations, the compression controller  950  may also make such an adjustment in response to receiving an external control signal. Such an external signal may be provided by another component coupled to the ANR circuit  2000  to provide such an external control signal in response to detecting a condition such as an exceptionally loud environmental noise sound that may cause one or both of the feedback-based and feedforward-based ANR functions to react unpredictably. 
         [0065]      FIG. 3   b  depicts another possible internal architecture  2200   b  of the ANR circuit  2000  in which a processing device accesses and executes stored machine-readable sequences of instructions that cause the processing device to manipulate digital data representing sounds in a manner that can be dynamically configured during operation of the ANR circuit  2000 . Such a use of a processing device enables pathways for movement of digital data of a topology to be defined through programming. More specifically, digital filters of varying quantities and/or types are able to be defined and instantiated in which each type of digital filter is based on a sequence of instructions. In employing the internal architecture  2200   b,  the ANR circuit  2000  incorporates the ADCs  210 ,  310  and  410 ; the processing device  510 ; the storage  520 ; the interface  530 ; a direct memory access (DMA) device  540 ; and the DAC  910 . Various possible variations may further incorporate one or more of the analog VGAs  125 ,  135  and  145 ; the ADC  955 ; and/or the audio amplifier  960 . The processing device  510  is coupled directly or indirectly via one or more buses to the storage  520 ; the interface  530 ; the DMA device  540 ; the ADCs  210 ,  310  and  410 ; and the DAC  910  to at least enable the processing device  510  to control their operation. The processing device  510  may also be similarly coupled to one or more of the analog VGAs  125 ,  135  and  145  (if present); and to the ADC  955  (if present). 
         [0066]    As in the internal architecture  2200   a,  the processing device  510  may be any of a variety of types of processing device, and once again, the storage  520  may be based on any of a variety of data storage technologies and may be made up of multiple components. Further, the interface  530  may support the coupling of the ANR circuit  2000  to one or more digital communications buses, and may provide one or more general purpose input/output (GPIO) electrical connections and/or analog electrical connections. The DMA device  540  may be based on a secondary processing device, discrete digital logic, a bus mastering sequencer, or any of a variety of other technologies. 
         [0067]    Stored within the storage  520  are one or more of a loading routine  522 , an ANR routine  525 , ANR settings  527 , ANR data  529 , a downsampling filter routine  553 , a biquad filter routine  555 , an interpolating filter routine  557 , a FIR filter routine  559 , and a VGA routine  561 . In some implementations, the processing device  510  accesses the storage  520  to read a sequence of instructions of the loading routine  522 , that when executed by the processing device  510 , causes the processing device  510  to operate the interface  530  to access the storage device  170  to retrieve one or more of the ANR routine  525 , the ANR settings  527 , the downsampling filter routine  553 , the biquad filter routine  555 , the interpolating filter routine  557 , the FIR routine  559  and the VGA routine  561 , and to store them in the storage  520 . In other implementations, one or more of these are stored in a nonvolatile portion of the storage  520  such that they need not be retrieved from the storage device  170 . 
         [0068]    As was the case in the internal architecture  2200   a,  the ADC  210  receives an analog signal from the feedback microphone  120 , the ADC  310  receives an analog signal from the feedforward microphone  130 , and the ADC  410  receives an analog signal from either the audio source  9400  or the communications microphone  140  (unless the use of one or more of the ADCs  210 ,  310  and  410  is obviated through the direct receipt of digital data). Again, one or more of the ADCs  210 ,  310  and  410  may receive their associated analog signals through one or more of the analog VGAs  125 ,  135  and  145 , respectively. As was also the case in the internal architecture  2200   a,  the DAC  910  converts digital data representing sounds to be acoustically output to an ear of a user of the personal ANR device  1000  into an analog signal, and the audio amplifier  960  amplifies this signal sufficiently to drive the acoustic driver  190  to effect the acoustic output of those sounds. 
         [0069]    However, unlike the internal architecture  2200   a  where digital data representing sounds were routed via an array of switching devices, such digital data is stored in and retrieved from the storage  520 . In some implementations, the processing device  510  repeatedly accesses the ADCs  210 ,  310  and  410  to retrieve digital data associated with the analog signals they receive for storage in the storage  520 , and repeatedly retrieves the digital data associated with the analog signal output by the DAC  910  from the storage  520  and provides that digital data to the DAC  910  to enable the creation of that analog signal. In other implementations, the DMA device  540  (if present) transfers digital data among the ADCs  210 ,  310  and  410 ; the storage  520  and the DAC  910  independently of the processing device  510 . In still other implementations, the ADCs  210 ,  310  and  410  and/or the DAC  910  incorporate “bus mastering” capabilities enabling each to write digital data to and/or read digital data from the storage  520  independently of the processing device  510 . The ANR data  529  is made up of the digital data retrieved from the ADCs  210 ,  310  and  410 , and the digital data provided to the DAC  910  by the processing device  510 , the DMA device  540  and/or bus mastering functionality. 
         [0070]    The downsampling filter routine  553 , the biquad filter routine  555 , the interpolating filter routine  557  and the FIR filter routine  559  are each made up of a sequence of instructions that cause the processing device  510  to perform a combination of calculations that define a downsampling filter, a biquad filter, an interpolating filter and a FIR filter, respectively. Further, among each of the different types of digital filters may be variants of those digital filters that are optimized for different data transfer rates, including and not limited to, differing bit widths of coefficients or differing quantities of taps. Similarly, the VGA routine  561  is made up of a sequence of instructions that cause the processing device  510  to perform a combination of calculations that define a VGA. Although not specifically depicted, a summing node routine may also be stored in the storage  520  made up of a sequence of instructions that similarly defines a summing node. 
         [0071]    The ANR routine  525  is made up of a sequence of instructions that cause the processing device  510  to create a signal processing topology having pathways incorporating varying quantities of the digital filters and VGAs defined by the downsampling filter routine  553 , the biquad filter routine  555 , the interpolating filter routine  557 , the FIR filter routine  559  and the VGA routine  561  to support feedback-based ANR, feedforward-based ANR and/or pass-through audio. The ANR routine  525  also causes the processing device  510  to perform the calculations defining each of the various filters and VGAs incorporated into that topology. Further, the ANR routine  525  either causes the processing device  510  to perform the moving of data among ADCs  210 ,  310  and  410 , the storage  520  and the DAC  910 , or causes the processing device  510  to coordinate the performance of such moving of data either by the DMA device  540  (if present) or by bus mastering operations performed by the ADCs  210 ,  310  and  410 , and/or the DAC  910 . 
         [0072]    The ANR settings  527  is made up of data defining topology characteristics (including selections of digital filters), filter coefficients, gain settings, clock frequencies, data transfer rates and/or data sizes. In some implementations, the topology characteristics may also define the characteristics of any summing nodes to be incorporated into the topology. The processing device  510  is caused by the ANR routine  525  to employ such data taken from the ANR settings  527  in creating a signal processing topology (including selecting digital filters), setting the filter coefficients for each digital filter incorporated into the topology, and setting the gains for each VGA incorporated into the topology. The processing device  510  may be further caused by the ANR routine  525  to employ such data from the ANR settings  527  in setting clock frequencies and/or data transfer rates for the ADCs  210 ,  310  and  410 ; for the digital filters incorporated into the topology; for the VGAs incorporated into the topology; and for the DAC  910 . 
         [0073]    In some implementations, the ANR settings  527  specify multiple sets of topology characteristics, filter coefficients, gain settings, clock frequencies and/or data transfer rates, of which different sets are used in response to different situations. In other implementations, execution of sequences of instructions of the ANR routine  525  causes the processing device  510  to derive different sets of filter coefficients, gain settings, clock frequencies and/or data transfer rates for a given signal processing topology in different situations. By way of example, the processing device  510  may be caused to operate the interface  530  to monitor a signal from the power source  180  that is indicative of the power available from the power source  180 , and to employ different sets of filter coefficients, gain settings, clock frequencies and/or data transfer rates in response to changes in the amount of available power. 
         [0074]    By way of another example, the processing device  510  may be caused to alter the provision of ANR to adjust the degree of ANR required in response to observed characteristics of one or more sounds. Where a reduction in the degree of attenuation and/or the range of frequencies of noise sounds attenuated is possible and/or desired, it may be possible to simplify the quantity and/or type of filters used in implementing feedback-based and/or feedforward-based ANR, and the processing device  510  may be caused to dynamically switch between different sets of filter coefficients, gain settings, clock frequencies and/or data transfer rates to perform such simplifying, with the added benefit of a reduction in power consumption. 
         [0075]    Therefore, in executing sequences of instructions of the ANR routine  525 , the processing device  510  is caused to retrieve data from the ANR settings  527  in preparation for adopting a signal processing topology defining the pathways to be employed by the processing device  510  in providing feedback-based ANR, feedforward-based ANR and pass-through audio. The processing device  510  is caused to instantiate multiple instances of digital filters, VGAs and/or summing nodes, employing filter coefficients, gain settings and/or other data from the ANR settings  527 . The processing device  510  is then further caused to perform the calculations defining each of those instances of digital filters, VGAs and summing nodes; to move digital data among those instances of digital filters, VGAs and summing nodes; and to at least coordinate the moving of digital data among the ADCs  210 ,  310  and  410 , the storage  520  and the DAC  910  in a manner that conforms to the data retrieved from the ANR settings  527 . At a subsequent time, the ANR routine  525  may cause the processing device  510  to change the signal processing topology, a digital filter, filter coefficients, gain settings, clock frequencies and/or data transfer rates during operation of the personal ANR device  1000 . It is largely in this way that the digital circuitry of the internal architecture  2200   b  is made dynamically configurable. Also, in this way, varying quantities and types of digital filters and/or digital VGAs may be positioned at various points along a pathway of a topology defined for a flow of digital data to modify sounds represented by that digital data and/or to derive new digital data representing new sounds, as will be explained in greater detail. 
         [0076]    In some implementations, the ANR routine  525  may cause the processing device  510  to give priority to operating the ADC  210  and performing the calculations of the digital filters, VGAs and/or summing nodes positioned along the pathway defined for the flow of digital data associated with feedback-based ANR. Such a measure may be taken in recognition of the higher sensitivity of feedback-based ANR to the latency between the detection of feedback reference sounds and the acoustic output of feedback anti-noise sounds. 
         [0077]    The processing device  510  may be further caused by the ANR routine  525  to monitor the sounds to be acoustically output for indications of the amplitude being too high, clipping, indications of clipping about to occur, and/or other audio artifacts actually occurring or indications of being about to occur. The processing device  510  may be caused to either directly monitor digital data provided to the DAC  910  or the analog signal output by the audio amplifier  960  (through the ADC  955 ) for such indications. In response to such an indication, the processing device  510  may be caused to operate one or more of the analog VGAs  125 ,  135  and  145  to adjust at least one amplitude of an analog signal, and/or may be caused to operate one or more of the VGAs based on the VGA routine  561  and positioned within a pathway of a topology to adjust the amplitude of at least one sound represented by digital data, as will be explained in greater detail. 
         [0078]      FIGS. 4   a  through  4   g  depict some possible signal processing topologies that may be adopted by the ANR circuit  2000  of the personal ANR device  1000  of  FIG. 1 . As previously discussed, some implementations of the personal ANR device  1000  may employ a variant of the ANR circuit  2000  that is at least partially programmable such that the ANR circuit  2000  is able to be dynamically configured to adopt different signal processing topologies during operation of the ANR circuit  2000 . Alternatively, other implementations of the personal ANR device  1000  may incorporate a variant of the ANR circuit  2000  that is substantially inalterably structured to adopt one unchanging signal processing topology. 
         [0079]    As previously discussed, separate ones of the ANR circuit  2000  are associated with each earpiece  100 , and therefore, implementations of the personal ANR device  1000  having a pair of the earpieces  100  also incorporate a pair of the ANR circuits  2000 . However, as those skilled in the art will readily recognize, other electronic components incorporated into the personal ANR device  1000  in support of a pair of the ANR circuits  2000 , such as the power source  180 , may not be duplicated. For the sake of simplicity of discussion and understanding, signal processing topologies for only a single ANR circuit  2000  are presented and discussed in relation to  FIGS. 4   a - g.    
         [0080]    As also previously discussed, different implementations of the personal ANR device  1000  may provide only one of either feedback-based ANR or feedforward-based ANR, or may provide both. Further, different implementations may or may not additionally provide pass-through audio. Therefore, although signal processing topologies implementing all three of feedback-based ANR, feedforward-based ANR and pass-through audio are depicted in  FIGS. 4   a - g,  it is to be understood that variants of each of these signal processing topologies are possible in which only one or the other of these two forms of ANR is provided, and/or in which pass-through audio is not provided. In implementations in which the ANR circuit  2000  is at least partially programmable, which of these two forms of ANR are provided and/or whether or not both forms of ANR are provided may be dynamically selectable during operation of the ANR circuit  2000 . 
         [0081]      FIG. 4   a  depicts a possible signal processing topology  2500   a  for which the ANR circuit  2000  may be structured and/or programmed. Where the ANR circuit  2000  adopts the signal processing topology  2500   a,  the ANR circuit  2000  incorporates at least the DAC  910 , the compression controller  950 , and the audio amplifier  960 . Depending, in part on whether one or both of feedback-based and feedforward-based ANR are supported, the ANR circuit  2000  further incorporates one or more of the ADCs  210 ,  310 ,  410  and/or  955 ; filter blocks  250 ,  350  and/or  450 ; and/or summing nodes  270  and/or  290 . 
         [0082]    Where the provision of feedback-based ANR is supported, the ADC  210  receives an analog signal from the feedback microphone  120  representing feedback reference sounds detected by the feedback microphone  120 . The ADC  210  digitizes the analog signal from the feedback microphone  120 , and provides feedback reference data corresponding to the analog signal output by the feedback microphone  120  to the filter block  250 . One or more digital filters within the filter block  250  are employed to modify the data from the ADC  210  to derive feedback anti-noise data representing feedback anti-noise sounds. The filter block  250  provides the feedback anti-noise data to the VGA  280 , possibly through the summing node  270  where feedforward-based ANR is also supported. 
         [0083]    Where the provision of feedforward-based ANR is also supported, the ADC  310  receives an analog signal from the feedforward microphone  130 , digitizes it, and provides feedforward reference data corresponding to the analog signal output by the feedforward microphone  130  to the filter block  350 . One or more digital filters within the filter block  350  are employed to modify the feedforward reference data received from the ADC  310  to derive feedforward anti-noise data representing feedforward anti-noise sounds. The filter block  350  provides the feedforward anti-noise data to the VGA  280 , possibly through the summing node  270  where feedback-based ANR is also supported. 
         [0084]    At the VGA  280 , the amplitude of one or both of the feedback and feedforward anti-noise sounds represented by the data received by the VGA  280  (either through the summing node  270 , or not) may be altered under the control of the compression controller  950 . The VGA  280  outputs its data (with or without amplitude alteration) to the DAC  910 , possibly through the summing nodes  290  where talk-through audio is also supported. 
         [0085]    In some implementations where pass-through audio is supported, the ADC  410  digitizes an analog signal representing pass-through audio received from the audio source  9400 , the communications microphone  140  or another source and provides the digitized result to the filter block  450 . In other implementations where pass-through audio is supported, the audio source  9400 , the communications microphone  140  or another source provides digital data representing pass-through audio to the filter block  450  without need of analog-to-digital conversion. One or more digital filters within the filter block  450  are employed to modify the digital data representing the pass-through audio to derive a modified variant of the pass-through audio data in which the pass-through audio may be re-equalized and/or enhanced in other ways. The filter block  450  provides the pass-through audio data to the summing node  290  where the pass-through audio data is combined with the data being provided by the VGA  280  to the DAC  910 . 
         [0086]    The analog signal output by the DAC  910  is provided to the audio amplifier  960  to be amplified sufficiently to drive the acoustic driver  190  to acoustically output one or more of feedback anti-noise sounds, feedforward anti-noise sounds and pass-through audio. The compression controller  950  controls the gain of the VGA  280  to enable the amplitude of sound represented by data output by one or both of the filter blocks  250  and  350  to be reduced in response to indications of impending instances of clipping, actual occurrences of clipping and/or other undesirable audio artifacts being detected by the compression controller  950 . The compression controller  950  may either monitor the data being provided to the DAC  910  by the summing node  290 , or may monitor the analog signal output of the audio amplifier  960  through the ADC  955 . 
         [0087]    As further depicted in  FIG. 4   a,  the signal processing topology  2500   a  defines multiple pathways along which digital data associated with feedback-based ANR, feedforward-based ANR and pass-through audio flow. Where feedback-based ANR is supported, the flow of feedback reference data and feedback anti-noise data among at least the ADC  210 , the filter block  250 , the VGA  280  and the DAC  910  defines a feedback-based ANR pathway  200 . Similarly, where feedforward-based ANR is supported, the flow of feedforward reference data and feedforward anti-noise data among at least the ADC  310 , the filter block  350 , the VGA  280  and the DAC  910  defines a feedforward-based ANR pathway  300 . Further, where pass-through audio is supported, the flow of pass-through audio data and modified pass-through audio data among at least the ADC  410 , the filter block  450 , the summing node  290  and the DAC  910  defines a pass-through audio pathway  400 . Where both feedback-based and feedforward-based ANR are supported, the pathways  200  and  300  both further incorporate the summing node  270 . Further, where pass-through audio is also supported, the pathways  200  and/or  300  incorporate the summing node  290 . 
         [0088]    In some implementations, digital data representing sounds may be clocked through all of the pathways  200 ,  300  and  400  that are present at the same data transfer rate. Thus, where the pathways  200  and  300  are combined at the summing node  270 , and/or where the pathway  400  is combined with one or both of the pathways  200  and  300  at the summing node  400 , all digital data is clocked through at a common data transfer rate, and that common data transfer rate may be set by a common synchronous data transfer clock. However, as is known to those skilled in the art and as previously discussed, the feedforward-based ANR and pass-through audio functions are less sensitive to latencies than the feedback-based ANR function. Further, the feedforward-based ANR and pass-through audio functions are more easily implemented with sufficiently high quality of sound with lower data sampling rates than the feedback-based ANR function. Therefore, in other implementations, portions of the pathways  300  and/or  400  may be operated at slower data transfer rates than the pathway  200 . Preferably, the data transfer rates of each of the pathways  200 ,  300  and  400  are selected such that the pathway  200  operates with a data transfer rate that is an integer multiple of the data transfer rates selected for the portions of the pathways  300  and/or  400  that are operated at slower data transfer rates. 
         [0089]    By way of example in an implementation in which all three of the pathways  200 ,  300  and  400  are present, the pathway  200  is operated at a data transfer rate selected to provide sufficiently low latency to enable sufficiently high quality of feedback-based ANR that the provision of ANR is not unduly compromised (e.g., by having anti-noise sounds out-of-phase with the noise sounds they are meant to attenuate, or instances of negative noise reduction such that more noise is actually being generated than attenuated, etc.), and/or sufficiently high quality of sound in the provision of at least the feedback anti-noise sounds. Meanwhile, the portion of the pathway  300  from the ADC  310  to the summing node  270  and the portion of the pathway  400  from the ADC  410  to the summing node  290  are both operated at lower data transfer rates (either the same lower data transfer rates or different ones) that still also enable sufficiently high quality of feedforward-based ANR in the pathway  300 , and sufficiently high quality of sound in the provision of the feedforward anti-noise through the pathway  300  and/or pass-through audio through the pathway  400 . 
         [0090]    In recognition of the likelihood that the pass-through audio function may be even more tolerant of a greater latency and a lower sampling rate than the feedforward-based ANR function, the data transfer rate employed in that portion of the pathway  400  may be still lower than the data transfer rate of that portion of the pathway  300 . To support such differences in transfer rates in one variation, one or both of the summing nodes  270  and  290  may incorporate sample-and-hold, buffering or other appropriate functionality to enable the combining of digital data received by the summing nodes  270  and  290  at different data transfer rates. This may entail the provision of two different data transfer clocks to each of the summing nodes  270  and  290 . Alternatively, to support such differences in transfer rates in another variation, one or both of the filter blocks  350  and  450  may incorporate an upsampling capability (perhaps through the inclusion of an interpolating filter or other variety of filter incorporating an upsampling capability) to increase the data transfer rate at which the filter blocks  350  and  450  provide digital data to the summing nodes  270  and  290 , respectively, to match the data transfer rate at which the filter block  250  provides digital data to the summing node  270 , and subsequently, to the summing node  290 . 
         [0091]    It may be that in some implementations, multiple power modes may be supported in which the data transfer rates of the pathways  300  and  400  are dynamically altered in response to the availability of power from the power source  180  and/or in response to changing ANR requirements. More specifically, the data transfer rates of one or both of the pathway  300  and  400  up to the points where they are combined with the pathway  200  may be reduced in response to an indication of diminishing power being available from the power supply  180  and/or in response to the processing device  510  detecting characteristics in sounds represented by digital data indicating that the degree of attenuation and/or range of frequencies of noise sounds attenuated by the ANR provided can be reduced. In making determinations of whether or not such reductions in data transfer rates are possible, the processing device  510  may be caused to evaluate the effects of such reductions in data transfer rates on quality of sound through one or more of the pathways  200 ,  300  and  400 , and/or the quality of feedback-based and/or feed-forward based ANR provided. 
         [0092]      FIG. 4   b  depicts a possible signal processing topology  2500   b  for which the ANR circuit  2000  may be structured and/or programmed. Where the ANR circuit  2000  adopts the signal processing topology  2500   b,  the ANR circuit  2000  incorporates at least the DAC  910 , the audio amplifier  960 , the ADC  210 , a pair of summing nodes  230  and  270 , and a pair of filter blocks  250  and  450 . The ANR circuit  2000  may further incorporate one or more of the ADC  410 , the ADC  310 , a filter block  350  and a summing node  370 . 
         [0093]    The ADC  210  receives and digitizes an analog signal from the feedback microphone  120  representing feedback reference sounds detected by the feedback microphone  120 , and provides corresponding feedback reference data to the summing node  230 . In some implementations, the ADC  410  digitizes an analog signal representing pass-through audio received from the audio source  9400 , the communications microphone  140  or another source and provides the digitized result to the filter block  450 . In other implementations, the audio source  9400 , the communications microphone  140  or another source provides digital data representing pass-through audio to the filter block  450  without need of analog-to-digital conversion. One or more digital filters within the filter block  450  are employed to modify the digital data representing the pass-through audio to derive a modified variant of the pass-through audio data in which the pass-through audio may be re-equalized and/or enhanced in other ways. One or more digital filters within the filter block  450  also function as a crossover that divides the modified pass-through audio data into higher and lower frequency sounds, with data representing the higher frequency sounds being output to the summing node  270 , and data representing the lower frequency sounds being output to the summing node  230 . In various implementations, the crossover frequency employed in the filter block  450  is dynamically selectable during operation of the ANR circuit  2000 , and may be selected to effectively disable the crossover function to cause data representing all frequencies of the modified pass-through audio to be output to either of the summing nodes  230  or  270 . In this way, the point at which the modified pass-through audio data is combined with data for the feedback ANR function within the signal processing topology  2500   a  can be made selectable. 
         [0094]    As just discussed, feedback reference data from the ADC  210  may be combined with data from the filter block  450  for the pass-through audio function (either the lower frequency sounds, or all of the modified pass-through audio) at the summing node  230 . The summing node  230  outputs the possibly combined data to the filter block  250 . One or more digital filters within the filter block  250  are employed to modify the data from summing node  230  to derive modified data representing at least feedback anti-noise sounds and possibly further-modified pass-through audio sounds. The filter block  250  provides the modified data to the summing node  270 . The summing node  270  combines the data from the filter block  450  that possibly represents higher frequency sounds of the modified pass-through audio with the modified data from the filter block  250 , and provides the result to the DAC  910  to create an analog signal. The provision of data by the filter block  450  to the summing node  270  may be through the summing node  370  where the provision of feedforward-based ANR is also supported. 
         [0095]    Where the crossover frequency employed in the filter block  450  is dynamically selectable, various characteristics of the filters making up the filter block  450  may also be dynamically configurable. By way of example, the number and/or type of digital filters making up the filter block  450  may be dynamically alterable, as well as the coefficients for each of those digital filters. Such dynamic configurability may be deemed desirable to correctly accommodate changes among having no data from the filter block  450  being combined with feedback reference data from the ADC  210 , having data from the filter block  450  representing lower frequency sounds being combined with feedback reference data from the ADC  210 , and having data representing all of the modified pass-through audio from the filter block  450  being combined with feedback reference data from the ADC  210 . 
         [0096]    Where the provision of feedforward-based ANR is also supported, the ADC  310  receives an analog signal from the feedforward microphone  130 , digitizes it, and provides feedforward reference data corresponding to the analog signal output by the feedforward microphone  130  to the filter block  350 . One or more digital filters within the filter block  350  are employed to modify the feedforward reference data received from the ADC  310  to derive feedforward anti-noise data representing feedforward anti-noise sounds. The filter block  350  provides the feedforward anti-noise data to the summing node  370  where the feedforward anti-noise data is possibly combined with data that may be provided by the filter block  450  (either the higher frequency sounds, or all of the modified pass-through audio). 
         [0097]    The analog signal output by the DAC  910  is provided to the audio amplifier  960  to be amplified sufficiently to drive the acoustic driver  190  to acoustically output one or more of feedback anti-noise sounds, feedforward anti-noise sounds and pass-through audio. 
         [0098]    As further depicted in  FIG. 4   b,  the signal processing topology  2500   b  defines its own variations of the pathways  200 ,  300  and  400  along which digital data associated with feedback-based ANR, feedforward-based ANR and pass-through audio, respectively, flow. In a manner not unlike the pathway  200  of the signal processing topology  2500   a,  the flow of feedback reference data and feedback anti-noise data among the ADC  210 , the summing nodes  230  and  270 , the filter block  250  and the DAC  910  defines the feedback-based ANR pathway  200  of the signal processing topology  2500   b.  Where feedforward-based ANR is supported, in a manner not unlike the pathway  300  of the signal processing topology  2500   a,  the flow of feedforward reference data and feedforward anti-noise data among the ADC  310 , the filter block  350 , the summing nodes  270  and  370 , and the DAC  910  defines the feedforward-based ANR pathway  300  of the signal processing topology  2500   b.  However, in a manner very much unlike the pathway  400  of the signal processing topology  2500   a,  the ability of the filter block  450  of the signal processing topology  2500   b  to split the modified pass-through audio data into higher frequency and lower frequency sounds results in the pathway  400  of the signal processing topology  2500   b  being partially split. More specifically, the flow of digital data from the ADC  410  to the filter block  450  is split at the filter block  450 . One split portion of the pathway  400  continues to the summing node  230 , where it is combined with the pathway  200 , before continuing through the filter block  250  and the summing node  270 , and ending at the DAC  910 . The other split portion of the pathway  400  continues to the summing node  370  (if present), where it is combined with the pathway  300  (if present), before continuing through the summing node  270  and ending at the DAC  910 . 
         [0099]    Also not unlike the pathways  200 ,  300  and  400  of the signal processing topology  2500   a,  the pathways  200 ,  300  and  400  of the signal processing topology  2500   b  may be operated with different data transfer rates. However, differences in data transfer rates between the pathway  400  and both of the pathways  200  and  300  would have to be addressed. Sample-and-hold, buffering or other functionality may be incorporated into each of the summing nodes  230 ,  270  and/or  370 . Alternatively and/or additionally, the filter block  350  may incorporate interpolation or other upsampling capability in providing digital data to the summing node  370 , and/or the filter block  450  may incorporate a similar capability in providing digital data to each of the summing nodes  230  and  370  (or  270 , if the pathway  300  is not present). 
         [0100]      FIG. 4   c  depicts another possible signal processing topology  2500   c  for which the ANR circuit  2000  may be structured and/or programmed. Where the ANR circuit  2000  adopts the signal processing topology  2500   c,  the ANR circuit  2000  incorporates at least the DAC  910 , the audio amplifier  960 , the ADC  210 , the summing node  230 , the filter blocks  250  and  450 , the VGA  280 , another summing node  290 , and the compressor  950 . The ANR circuit  2000  may further incorporate one or more of the ADC  410 , the ADC  310 , the filter block  350 , the summing node  270 , and the ADC  955 . The signal processing topologies  2500   b  and  2500   c  are similar in numerous ways. However, a substantial difference between the signal processing topologies  2500   b  and  2500   c  is the addition of the compressor  950  in the signal processing topology  2500   c  to enable the amplitudes of the sounds represented by data output by both of the filter blocks  250  and  350  to be reduced in response to the compressor  950  detecting actual instances or indications of impending instances of clipping and/or other undesirable audio artifacts. 
         [0101]    The filter block  250  provides its modified data to the VGA  280  where the amplitude of the sounds represented by the data provided to the VGA  280  may be altered under the control of the compression controller  950 . The VGA  280  outputs its data (with or without amplitude alteration) to the summing node  290 , where it may be combined with data that may be output by the filter block  450  (perhaps the higher frequency sounds of the modified pass-through audio, or perhaps the entirety of the modified pass-through audio). In turn, the summing node  290  provides its output data to the DAC  910 . Where the provision of feedforward-based ANR is also supported, the data output by the filter block  250  to the VGA  280  is routed through the summing node  270 , where it is combined with the data output by the filter block  350  representing feedforward anti-noise sounds, and this combined data is provided to the VGA  280 . 
         [0102]      FIG. 4   d  depicts another possible signal processing topology  2500   d  for which the ANR circuit  2000  may be structured and/or programmed. Where the ANR circuit  2000  adopts the signal processing topology  2500   d,  the ANR circuit  2000  incorporates at least the DAC  910 , the compression controller  950 , the audio amplifier  960 , the ADC  210 , the summing nodes  230  and  290 , the filter blocks  250  and  450 , the VGA  280 , and still other VGAs  445 ,  455  and  460 . The ANR circuit  2000  may further incorporate one or more of the ADCs  310  and/or  410 , the filter block  350 , the summing node  270 , the ADC  955 , and still another VGA  360 . The signal processing topologies  2500   c  and  2500   d  are similar in numerous ways. However, a substantial difference between the signal processing topologies  2500   c  and  2500   d  is the addition of the ability to direct the provision of the higher frequency sounds of the modified pass-through audio to be combined with other audio at either or both of two different locations within the signal processing topology  2500   d.    
         [0103]    One or more digital filters within the filter block  450  are employed to modify the digital data representing the pass-through audio to derive a modified variant of the pass-through audio data and to function as a crossover that divides the modified pass-through audio data into higher and lower frequency sounds. Data representing the lower frequency sounds are output to the summing node  230  through the VGA  445 . Data representing the higher frequency sounds are output both to the summing node  230  through the VGA  455  and to the DAC  910  through the VGA  460 . The VGAs  445 ,  455  and  460  are operable both to control the amplitudes of the lower frequency and higher frequency sounds represented by the data output by the filter block  450 , and to selectively direct the flow of the data representing the higher frequency sounds. However, as has been previously discussed, the crossover functionality of the filter block  450  may be employed to selectively route the entirety of the modified pass-through audio to one or the other of the summing node  230  and the DAC  910 . 
         [0104]    Where the provision of feedforward-based ANR is also supported, the possible provision of higher frequency sounds (or perhaps the entirety of the modified pass-through audio) by the filter block  450  through the VGA  460  and to the DAC  910  may be through the summing node  290 . The filter block  350  provides the feedforward anti-noise data to the summing node  270  through the VGA  360 . 
         [0105]      FIG. 4   e  depicts another possible signal processing topology  2500   e  for which the ANR circuit  2000  may be structured and/or programmed. Where the ANR circuit  2000  adopts the signal processing topology  2500   e,  the ANR circuit  2000  incorporates at least the DAC  910 ; the audio amplifier  960 ; the ADCs  210  and  310 ; the summing nodes  230 ,  270  and  370 ; the filter blocks  250 ,  350  and  450 ; the compressor  950 ; and a pair of VGAs  240  and  340 . The ANR circuit  2000  may further incorporate one or both of the ADCs  410  and  955 . The signal processing topologies  2500   b,    2500   c  and  2500   e  are similar in numerous ways. The manner in which the data output by each of the filter blocks  250 ,  350  and  450  are combined in the signal processing topology  2500   e  is substantially similar to that of the signal processing topology  2500   b.  Also, like the signal processing topology  2500   c,  the signal processing topology  2500   e  incorporates the compression controller  950 . However, a substantial difference between the signal processing topologies  2500   c  and  2500   e  is the replacement of the single VGA  280  in the signal processing topology  2500   c  for the separately controllable VGAs  240  and  340  in the signal processing topology  2500   e.    
         [0106]    The summing node  230  provides data representing feedback reference sounds possibly combined with data that may be output by the filter block  450  (perhaps the lower frequency sounds of the modified pass-through audio, or perhaps the entirety of the modified pass-through audio) to the filter block  250  through the VGA  240 , and the ADC  310  provides data representing feedforward reference sounds to the filter block  350  through the VGA  340 . The data output by the filter block  350  is combined with data that may be output by the filter block  450  (perhaps the higher frequency sounds of the modified pass-through audio, or perhaps the entirety of the modified pass-through audio) at the summing node  370 . In turn, the summing node  370  provides its data to the summing node  270  to be combined with data output by the filter block  250 . The summing node  270 , in turn, provides its combined data to the DAC  910 . 
         [0107]    The compression controller  950  controls the gains of the VGAs  240  and  340 , to enable the amplitude of the sounds represented by data output by the summing node  230  and the ADC  310 , respectively, to be reduced in response to actual instances or indications of upcoming instances of clipping and/or other undesirable audio artifacts being detected by the compression controller  950 . The gains of the VGAs  240  and  340  may be controlled in a coordinated manner, or may be controlled entirely independently of each other. 
         [0108]      FIG. 4   f  depicts another possible signal processing topology  2500   f  for which the ANR circuit  2000  may be structured and/or programmed. Where the ANR circuit  2000  adopts the signal processing topology  2500   f,  the ANR circuit  2000  incorporates at least the DAC  910 ; the audio amplifier  960 ; the ADCs  210  and  310 ; the summing nodes  230 ,  270  and  370 ; the filter blocks  250 ,  350  and  450 ; the compressor  950 ; and the VGAs  125  and  135 . The ANR circuit  2000  may further incorporate one or both of the ADCs  410  and  955 . The signal processing topologies  2500   e  and  2500   f  are similar in numerous ways. However, a substantial difference between the signal processing topologies  2500   e  and  2500   f  is the replacement of the pair of VGAs  240  and  340  in the signal processing topology  2500   e  for the VGAs  125  and  135  in the signal processing topology  2500   f.    
         [0109]    The VGAs  125  and  135  positioned at the analog inputs to the ADCs  210  and  310 , respectively, are analog VGAs, unlike the VGAs  240  and  340  of the signal processing topology  2500   e.  This enables the compression controller  950  to respond to actual occurrences and/or indications of soon-to-occur instances of clipping and/or other audio artifacts in driving the acoustic driver  190  by reducing the amplitude of one or both of the analog signals representing feedback and feedforward reference sounds. This may be deemed desirable where it is possible for the analog signals provided to the ADCs  210  and  310  to be at too great an amplitude such that clipping at the point of driving the acoustic driver  190  might be more readily caused to occur. The provision of the ability to reduce the amplitude of these analog signals (and perhaps also including the analog signal provided to the ADC  410  via the VGA  145  depicted elsewhere) may be deemed desirable to enable balancing of amplitudes between these analog signals, and/or to limit the numeric values of the digital data produced by one or more of the ADCs  210 ,  310  and  410  to lesser magnitudes to reduce storage and/or transmission bandwidth requirements. 
         [0110]      FIG. 4   g  depicts another possible signal processing topology  2500   g  for which the ANR circuit  2000  may be programmed or otherwise structured. Where the ANR circuit  2000  adopts the signal processing topology  2500   g,  the ANR circuit  2000  incorporates at least the compression controller  950 , the DAC  910 , the audio amplifier  960 , the ADCs  210  and  310 , a pair of VGAs  220  and  320 , the summing nodes  230  and  270 , the filter blocks  250  and  350 , another pair of VGAs  355  and  360 , and the VGA  280 . The ANR circuit  2000  may further incorporate one or more of the ADC  410 , the filter block  450 , still another VGA  460 , the summing node  290 , and the ADC  955 . 
         [0111]    The ADC  210  receives an analog signal from the feedback microphone  120  and digitizes it, before providing corresponding feedback reference data to the VGA  220 . The VGA  220  outputs the feedback reference data, possibly after modifying its amplitude, to the summing node  230 . Similarly, the ADC  310  receives an analog signal from the feedforward microphone  130  and digitizes it, before providing corresponding feedforward reference data to the VGA  320 . The VGA  320  outputs the feedforward reference data, possibly after modifying its amplitude, to the filter block  350 . One or more digital filters within the filter block  350  are employed to modify the feedforward reference data to derive feedforward anti-noise data representing feedforward anti-noise sounds, and the filter block  350  provides the feedforward anti-noise data to both of the VGAs  355  and  360 . In various implementations, the gains of the VGAs  355  and  360  are dynamically selectable and can be operated in a coordinated manner like a three-way switch to enable the feedforward anti-noise data to be selectively provided to either of the summing nodes  230  and  270 . Thus, where the feedforward anti-noise data is combined with data related to feedback ANR within the signal processing topology  2500   g  is made selectable. 
         [0112]    Therefore, depending on the gains selected for the VGAs  355  and  360 , the feedforward anti-noise data from the filter block  350  may be combined with the feedback reference data from the ADC  210  at the summing node  230 , or may be combined with feedback anti-noise data derived by the filter block  250  from the feedback reference data at the summing node  270 . If the feedforward anti-noise data is combined with the feedback reference data at the summing node  230 , then the filter block  250  derives data representing a combination of feedback anti-noise sounds and further-modified feedforward anti-noise sounds, and this data is provided to the VGA  280  through the summing node  270  at which no combining of data occurs. Alternatively, if the feedforward anti-noise data is combined with the feedback anti-noise data at the summing node  270 , then the feedback anti-noise data will have been derived by the filter block  250  from the feedback reference data received through the summing node  230  at which no combining of data occurs, and the data resulting from the combining at the summing node  270  is provided to the VGA  280 . With or without an alteration in amplitude, the VGA  280  provides whichever form of combined data is received from the summing node  270  to the DAC  910  to create an analog signal. This provision of this combined data by the VGA  280  may be through the summing node  290  where the provision of pass-through audio is also supported. 
         [0113]    Where the provision of pass-through audio is supported, the audio source  9400  may provide an analog signal representing pass-through audio to be acoustically output to a user, and the ADC  410  digitizes the analog signal and provides pass-through audio data corresponding to the analog signal to the filter block  450 . Alternatively, where the audio source  9400  provides digital data representing pass-through audio, such digital data may be provided directly to the filter block  450 . One or more digital filters within the filter block  450  may be employed to modify the digital data representing the pass-through audio to derive a modified variant of the pass-through audio data that may be re-equalized and/or enhanced in other ways. The filter block  450  provides the modified pass-through audio data to the VGA  460 , and either with or without altering the amplitude of the pass-through audio sounds represented by the modified pass-through audio data, the VGA  460  provides the modified pass-through audio data to the DAC  910  through the summing node  290 . 
         [0114]    The compression controller  950  controls the gain of the VGA  280  to enable the amplitude of whatever combined form of feedback and feedforward anti-noise sounds are received by the VGA  280  to be reduced under the control of the compression controller  950  in response to actual occurrences and/or indications of impending instances of clipping and/or other audio artifacts. 
         [0115]      FIGS. 5   a  through  5   e  depict some possible filter block topologies that may be employed in creating one or more blocks of filters (such as filter blocks  250 ,  350  and  450 ) within signal processing topologies adopted by the ANR circuit  2000  (such as the signal processing topologies  2500   a - g ). It should be noted that the designation of a multitude of digital filters as a “filter block” is an arbitrary construct meant to simplify the earlier presentation of signal processing topologies. In truth, the selection and positioning of one or more digital filters at any point along any of the pathways (such as the pathways  200 ,  300  and  400 ) of any signal processing topology may be accomplished in a manner identical to the selection and positioning of VGAs and summing nodes. Therefore, it is entirely possible for various digital filters to be positioned along a pathway for the movement of data in a manner in which those digital filters are interspersed among VGAs and/or summing nodes such that no distinguishable block of filters is created. Or, as will be illustrated, it is entirely possible for a filter block to incorporate a summing node or other component as part of the manner in which the filters of a filter block are coupled as part of the filter block topology of a filter block. 
         [0116]    However, as previously discussed, multiple lower-order digital filters may be combined in various ways to perform the equivalent function of one or more higher-order digital filters. Thus, although the creation of distinct filter blocks is not necessary in defining a pathway having multiple digital filters, it can be desirable in numerous situations. Further, the creation of a block of filters at a single point along a pathway can more easily enable alterations in the characteristics of filtering performed in that pathway. By way of example, multiple lower-order digital filters connected with no other components interposed between them can be dynamically configured to cooperate to perform any of a variety of higher-order filter functions by simply changing their coefficients and/or changing the manner in which they are interconnected. Also, in some implementations, such close interconnection of digital filters may ease the task of dynamically configuring a pathway to add or remove digital filters with a minimum of changes to the interconnections that define that pathway. 
         [0117]    It should be noted that the selections of types of filters, quantities of filters, interconnections of filters and filter block topologies depicted in each of  FIGS. 5   a  through  5   e  are meant to serve as examples to facilitate understanding, and should not be taken as limiting the scope of what is described or the scope of what is claimed herein. 
         [0118]      FIG. 5   a  depicts a possible filter block topology  3500   a  for which the ANR circuit  2000  may be structured and/or programmed to define a filter block, such as one of the filter blocks  250 ,  350  and  450 . The filter block topology  3500   a  is made up of a serial chain of digital filters with a downsampling filter  652  at its input; biquad filters  654 ,  655  and  656 ; and a FIR filter  658  at its output. 
         [0119]    As more explicitly depicted in  FIG. 5   a,  in some implementations, the ANR circuit  2000  employs the internal architecture  2200   a  such that the ANR circuit  2000  incorporates the filter bank  550  incorporating multitudes of the downsampling filters  552 , the biquad filters  554 , and the FIR filters  558 . One or more of each of the downsampling filters  552 , biquad filters  554  and FIR filters  558  may be interconnected in any of a number of ways via the switch array  540 , including in a way that defines the filter block topology  3500   a.  More specifically, the downsampling filter  652  is one of the downsampling filters  552 ; the biquad filters  654 ,  655  and  656  are each one of the biquad filters  554 ; and the FIR filter  658  is one of the FIR filters  558 . 
         [0120]    Alternatively, and as also more explicitly depicted in  FIG. 5   a,  in other implementations, the ANR circuit  2000  employs the internal architecture  2200   b  such that the ANR circuit  2000  incorporates a storage  520  in which is stored the downsampling filter routine  553 , the biquad filter routine  555  and the FIR filter routine  559 . Varying quantities of downsampling, biquad and/or FIR filters may be instantiated within available storage locations of the storage  520  with any of a variety of interconnections defined between them, including quantities of filters and interconnections that define the filter block topology  3500   a.  More specifically, the downsampling filter  652  is an instance of the downsampling filter routine  553 ; the biquad filters  654 ,  655  and  656  are each instances of the biquad filter routine  555 ; and the FIR filter  658  is an instance of the FIR filter routine  559 . 
         [0121]    As previously discussed, power conservation and/or other benefits may be realized by employing different data transfer rates along different pathways of digital data representing sounds in a signal processing topology. In support of converting between different data transfer rates, including where one pathway operating at one data transfer rate is coupled to another pathway operating at another data transfer rate, different data transfer clocks may be provided to different ones of the digital filters within a filter block, and/or one or more digital filters within a filter block may be provided with multiple data transfer clocks. 
         [0122]    By way of example,  FIG. 5   a  depicts a possible combination of different data transfer rates that may be employed within the filter block topology  3500   a  to support digital data being received at one data transfer rate, digital data being transferred among these digital filters at another data transfer rate, and digital data being output at still another data transfer rate. More specifically, the downsampling filter  652  receives digital data representing a sound at a data transfer rate  672 , and at least downsamples that digital data to a lower data transfer rate  675 . The lower data transfer rate  675  is employed in transferring digital data among the downsampling filter  652 , the biquad filters  654 - 656 , and the FIR filter  658 . The FIR filter  658  at least upsamples the digital data that it receives from the lower data transfer rate  675  to a higher data transfer rate  678  as that digital data is output by the filter block to which the digital filters in the filter block topology  3500   a  belong. Many other possible examples of the use of more than one data transfer rate within a filter block and the possible corresponding need to employ multiple data transfer clocks within a filter block will be clear to those skilled in the art. 
         [0123]      FIG. 5   b  depicts a possible filter block topology  3500   b  that is substantially similar to the filter block topology  3500   a,  but in which the FIR filter  658  of the filter block topology  3500   a  has been replaced with an interpolating filter  657 . Where the internal architecture  2200   a  is employed, such a change from the filter block topology  3500   a  to the filter block topology  3500   b  entails at least altering the configuration of the switch array  540  to exchange one of the FIR filters  558  with one of the interpolating filters  556 . Where the internal architecture  2200   b  is employed, such a change entails at least replacing the instantiation of the FIR filter routine  559  that provides the FIR filter  658  with an instantiation of the interpolating filter routine  557  to provide the interpolating filter  657   
         [0124]      FIG. 5   c  depicts a possible filter block topology  3500   c  that is made up of the same digital filters as the filter block topology  3500   b,  but in which the interconnections between these digital filters have been reconfigured into a branching topology to provide two outputs, whereas the filter block topology  3500   b  had only one. Where the internal architecture  2200   a  is employed, such a change from the filter block topology  3500   b  to the filter block topology  3500   c  entails at least altering the configuration of the switch array  540  to disconnect the input to the biquad filter  656  from the output of the biquad filter  655 , and to connect that input to the output of the downsampling filter  652 , instead. Where the internal architecture  2200   b  is employed, such a change entails at least altering the instantiation of biquad filter routine  555  that provides the biquad filter  656  to receive its input from the instantiation of the downsampling filter routine  553  that provides the downsampling filter  652 . The filter block topology  3500   c  may be employed where it is desired that a filter block be capable of providing two different outputs in which data representing audio provided at the input is altered in different ways to create two different modified versions of that data, such as in the case of the filter block  450  in each of the signal processing topologies  2500   b - f.    
         [0125]      FIG. 5   d  depicts another possible filter block topology  3500   d  that is substantially similar to the filter block topology  3500   a,  but in which the biquad filters  655  and  656  have been removed to shorten the chain of digital filters from the quantity of five in the filter block topology  3500   a  to a quantity of three. 
         [0126]      FIG. 5   e  depicts another possible filter block topology  3500   e  that is made up of the same digital filters as the filter block topology  3500   b,  but in which the interconnections between these digital filters have been reconfigured to put the biquad filters  654 ,  655  and  656  in a parallel configuration, whereas these same filters were in a serial chain configuration in the filter block topology  3500   b.  As depicted, the output of the downsampling filter  652  is coupled to the inputs of all three of the biquad filters  654 ,  655  and  656 , and the outputs of all three of these biquad filters are coupled to the input of the interpolating filter  657  through an additionally incorporated summing node  659 . 
         [0127]    Taken together, the  FIGS. 5   a  through  5   e  depict the manner in which a given filter block topology of a filter block is dynamically configurable to so as to allow the types of filters, quantities of filters and/or interconnections of digital filters to be altered during the operation of a filter block. However, as those skilled in the art will readily recognize, such changes in types, quantities and interconnections of digital filters are likely to require corresponding changes in filter coefficients and/or other settings to be made to achieve the higher-order filter function sought to be achieved with such changes. As will be discussed in greater detail, to avoid or at least mitigate the creation of audible distortions or other undesired audio artifacts arising from making such changes during the operation of the personal ANR device, such changes in interconnections, quantities of components (including digital filters), types of components, filter coefficients and/or VGA gain values are ideally buffered so as to enable their being made in a manner coordinated in time with one or more data transfer rates. 
         [0128]    The dynamic configurability of both of the internal architectures  2200   a  and  2200   b,  as exemplified throughout the preceding discussion of dynamically configurable signal processing topologies and dynamically configurable filter block topologies, enables numerous approaches to conserving power and to reducing audible artifacts caused by the introduction of microphone self noise, quantization errors and other influences arising from components employed in the personal ANR device  1000 . Indeed, there can be a synergy between achieving both goals, since at least some measures taken to reduce audible artifacts generated by the components of the personal ANR device  1000  can also result in reductions in power consumption. Reductions in power consumption can be of considerable importance given that the personal ANR device  1000  is preferably powered from a battery or other portable source of electric power that is likely to be somewhat limited in ability to provide electric power. 
         [0129]    In either of the internal architectures  2200   a  and  2200   b,  the processing device  510  may be caused by execution of a sequence of instructions of the ANR routine  525  to monitor the availability of power from the power source  180 . Alternatively and/or additionally, the processing device  510  may be caused to monitor characteristics of one or more sounds (e.g., feedback reference and/or anti-noise sounds, feedforward reference and/or anti-noise sounds, and/or pass-through audio sounds) and alter the degree of ANR provided in response to the characteristics observed. As those familiar with ANR will readily recognize, it is often the case that providing an increased degree of ANR often requires the implementation of a more complex transfer function, which often requires a greater number of filters and/or more complex types of filters to implement, and this in turn, often leads to greater power consumption. Analogously, a lesser degree of ANR often requires the implementation of a simpler transfer function, which often requires fewer and/or simpler filters, which in turn, often leads to less power consumption. 
         [0130]    Further, there can arise situations, such as an environment with relatively low environmental noise levels or with environmental noise sounds occurring within a relatively narrow range of frequencies, where the provision of a greater degree of ANR can actually result in the components used in providing the ANR generating noise sounds greater than the attenuated environmental noise sounds. Still further, and as will be familiar to those skilled in the art of feedback-based ANR, under some circumstances, providing a considerable degree of feedback-based ANR can lead to instability as undesirable audible feedback noises are produced. 
         [0131]    In response to either an indication of diminishing availability of electric power or an indication that a lesser degree of ANR is needed (or is possibly more desirable), the processing device  510  may disable one or more functions (including one or both of feedback-based and feedforward-based ANR), lower data transfer rates of one or more pathways, disable branches within pathways, lower data transfer rates between digital filters within a filter block, replace digital filters that consume more power with digital filters that consume less power, reduce the complexity of a transfer function employed in providing ANR, reduce the overall quantity of digital filters within a filter block, and/or reduce the gain to which one or more sounds are subjected by reducing VGA gain settings and/or altering filter coefficients. However, in taking one or more of these or other similar actions, the processing device  510  may be further caused by the ANR routine  525  to estimate a degree of reduction in the provision of ANR that balances one or both of the goals of reducing power consumption and avoiding the provision of too great a degree of ANR with one or both of the goals of maintaining a predetermined desired degree of quality of sound and quality of ANR provided to a user of the personal ANR device  1000 . A minimum data transfer rate, a maximum signal-to-noise ratio or other measure may be used as the predetermined degree of quality or ANR and/or sound. 
         [0132]    As an example, and referring back to the signal processing topology  2500   a  of  FIG. 4   a  in which the pathways  200 ,  300  and  400  are explicitly depicted, a reduction in the degree of ANR provided and/or in the consumption of power may be realized through turning off one or more of the feedback-based ANR, feedforward-based ANR and pass-through audio functions. This would result in at least some of the components along one or more of the pathways  200 ,  300  and  400  either being operated to enter a low power state in which operations involving digital data would cease within those components, or being substantially disconnected from the power source  180 . A reduction in power consumption and/or degree of ANR provided may also be realized through lowering the data transfer rate(s) of at least portions of one or more of the pathways  200 ,  300  and  400 , as previously discussed in relation to  FIG. 4   a.    
         [0133]    As another example, and referring back to the signal processing topology  2500   b  of  FIG. 4   b  in which the pathways  200 ,  300  and  400  are also explicitly depicted, a reduction in power consumption and/or in the complexity of transfer functions employed may be realized through turning off the flow of data through one of the branches of the split in the pathway  400 . More specifically, and as previously discussed in relation to  FIG. 4   b,  the crossover frequency employed by the digital filters within the filter block  450  to separate the modified pass-through audio into higher frequency and lower frequency sounds may be selected to cause the entirety of the modified pass-through audio to be directed towards only one of the branches of the pathway  400 . This would result in discontinuing of the transfer of modified pass-through audio data through one or the other of the summing nodes  230  and  370 , thereby enabling a reduction in power consumption and/or in the introduction of noise sounds from components by allowing the combining function of one or the other of these summing nodes to be disabled or at least to not be utilized. Similarly, and referring back to the signal processing topology  2500   d  of  FIG. 4   d  (despite the lack of explicit marking of its pathways), either the crossover frequency employed by the filter block  450  or the gain settings of the VGAs  445 ,  455  and  460  may be selected to direct the entirety of the modified pass-through audio data down a single one of the three possible pathway branches into which each of these VGAs lead. Thus, a reduction in power consumption and/or in the introduction of noise sounds would be enabled by allowing the combining function of one or the other of the summing nodes  230  and  290  to be disabled or at least not be utilized. Still further, one or more of the VGAs  445 ,  455  and  460  through which modified pass-through audio data is not being transferred may be disabled. 
         [0134]    As still another example, and referring back to the filter block topology  3500   a  of  FIG. 5   a  in which the allocation of three data transfer rates  672 ,  675  and  678  are explicitly depicted, a reduction in the degree of ANR provided and/or in power consumption may be realized through lowering one or more of these data transfer rates. More specifically, within a filter block adopting the filter block topology  3500   a,  the data transfer rate  675  at which digital data is transferred among the digital filters  652 ,  654 - 656  and  658  may be reduced. Such a change in a data transfer rate may also be accompanied by exchanging one or more of the digital filters for variations of the same type of digital filter that are better optimized for lower bandwidth calculations. As will be familiar to those skilled in the art of digital signal processing, the level of calculation precision required to maintain a desired predetermined degree of quality of sound and/or quality of ANR in digital processing changes as sampling rate changes. Therefore, as the data transfer rate  675  is reduced, one or more of the biquad filters  654 - 656  which may have been optimized to maintain a desired degree of quality of sound and/or desired degree of quality of ANR at the original data transfer rate may be replaced with other variants of biquad filter that are optimized to maintain substantially the same quality of sound and/or ANR at the new lower data transfer rate with a reduced level of calculation precision that also reduces power consumption. This may entail the provision of different variants of one or more of the different types of digital filter that employ coefficient values of differing bit widths and/or incorporate differing quantities of taps. 
         [0135]    As still other examples, and referring back to the filter block topologies  3500   c  and  3500   d  of  FIGS. 5   c  and  5   d,  respectively, as well as to the filter block topology  3500   a,  a reduction in the degree of ANR provided and/or in power consumption may be realized through reducing the overall quantity of digital filters employed in a filter block. More specifically, the overall quantity of five digital filters in the serial chain of the filter block topology  3500   a  may be reduced to the overall quantity of three digital filters in the shorter serial chain of the filter block topology  3500   d.  As those skilled in the art would readily recognize, such a change in the overall quantity of digital filters would likely need to be accompanied by a change in the coefficients provided to the one or more of the digital filters that remain, since it is likely that the transfer function(s) performed by the original five digital filters would have to be altered or replaced by transfer function(s) that are able to be performed with the three digital filters that remain. Also more specifically, the overall quantity of five digital filters in the branching topology of the filter block topology  3500   c  may be reduced to an overall quantity of three digital filters by removing or otherwise deactivating the filters of one of the branches (e.g., the biquad filter  656  and the interpolating filter  657  of one branch that provides one of the two outputs). This may be done in concert with selecting a crossover frequency for a filter block providing a crossover function to effectively direct all frequencies of a sound represented by digital data to only one of the two outputs, and/or in concert with operating one or more VGAs external to a filter block to remove or otherwise cease the transfer of digital data through a branch of a signal processing topology. 
         [0136]    Reductions in data transfer rates may be carried out in various ways in either of the internal architectures  2200   a  and  2200   b.  By way of example in the internal architecture  2200   a,  various ones of the data transfer clocks provided by the clock bank  570  may be directed through the switch array  540  to differing ones of the digital filters, VGAs and summing nodes of a signal processing topology and/or filter block topology to enable the use of multiple data transfer rates and/or conversions between different data transfer rates by one or more of those components. By way of example in the internal architecture  2200   b,  the processing device  510  may be caused to execute the sequences of instructions of the various instantiations of digital filters, VGAs and summing nodes of a signal processing topology and/or filter block topology at intervals of differing lengths of time. Thus, the sequences of instructions for one instantiation of a given component are executed at more frequent intervals to support a higher data transfer rate than the sequences of instructions for another instantiation of the same component where a lower data transfer rate is supported. 
         [0137]    As yet another example, and referring back to any of the earlier-depicted signal processing topologies and/or filter block topologies, a reduction in the degree of ANR provided and/or in power consumption may be realized through the reduction of the gain to which one or more sounds associated with the provision of ANR (e.g., feedback reference and/or anti-noise sounds, or feedforward reference and/or anti-noise sounds). Where a VGA is incorporated into at least one of a feedback-based ANR pathway and a feedforward-based ANR pathway, the gain setting of that VGA may be reduced. Alternatively and/or additionally, and depending on the transfer function implemented by a given digital filter, one or more coefficients of that digital filter may be altered to reduce the gain imparted to whatever sounds are represented by the digital data output by that digital filter. As will be familiar to those skilled in the art, reducing a gain in a pathway can reduce the perceptibility of noise sounds generated by components. In a situation where there is relatively little in the way of environmental noise sounds, noise sounds generated by components can become more prevalent, and thus, reducing the noise sounds generated by the components can become more important than generating anti-noise sounds to attenuate what little in the way of environmental noise sounds may be present. In some implementations, such reduction(s) in gain in response to relatively low environmental noise sound levels may enable the use of lower cost microphones. 
         [0138]    In some implementations, performing such a reduction in gain at some point along a feedback-based ANR pathway may prove more useful than along a feedforward-based ANR pathway, since environmental noise sounds tend to be more attenuated by the PNR provided by the personal ANR device before ever reaching the feedback microphone  120 . As a result of the feedback microphone  120  tending to be provided with weaker variants of environmental noise sounds than the feedforward microphone  130 , the feedback-based ANR function may be more easily susceptible to a situation in which noise sounds introduced by components become more prevalent than environmental noise sounds at times when there is relatively little in the way of environmental noise sounds. A VGA may be incorporated into a feedback-based ANR pathway to perform this function by normally employing a gain value of 1 which would then be reduced to ½ or to some other preselected lower value in response to the processing device  510  and/or another processing device external to the ANR circuit  2000  and to which the ANR circuit  2000  is coupled determining that environmental noise levels are low enough that noise sounds generated by components in the feedback-based ANR pathway are likely to be significant enough that such a gain reduction is more advantageous than the production of feedback anti-noise sounds. 
         [0139]    The monitoring of characteristics of environmental noise sounds as part of determining whether or not changes in ANR settings are to be made may entail any of a number of approaches to measuring the strength, frequencies and/or other characteristics of the environmental noise sounds. In some implementations, a simple sound pressure level (SPL) or other signal energy measurement without weighting may be taken of environmental noise sounds as detected by the feedback microphone  120  and/or the feedforward microphone  130  within a preselected range of frequencies. Alternatively, the frequencies within the preselected range of frequencies of a SPL or other signal energy measurement may subjected to the widely known and used “A-weighted” frequency weighting curve developed to reflect the relative sensitivities of the average human ear to different audible frequencies. 
         [0140]      FIGS. 6   a  through  6   c  depict aspects and possible implementations of triple-buffering both to enable synchronized ANR setting changes and to enable a failsafe response to an occurrence and/or to indications of a likely upcoming occurrence of an out-of-bound condition, including and not limited to, clipping and/or excessive amplitude of acoustically output sounds, production of a sound within a specific range of frequencies that is associated with a malfunction, instability of at least feedback-based ANR, or other condition that may generate undesired or uncomfortable acoustic output. Each of these variations of triple-buffering incorporate at least a trio of buffers  620   a,    620   b  and  620   c.  In each depicted variation of triple-buffering, two of the buffers  620   a  and  620   b  are alternately employed during normal operation of the ANR circuit  2000  to synchronously update desired ANR settings “on the fly,” including and not limited to, topology interconnections, data clock settings, data width settings, VGA gain settings, and filter coefficient settings. Also, in each depicted variation of triple-buffering, the third buffer  620   c  maintains a set of ANR settings deemed to be “conservative” or “failsafe” settings that may be resorted to bring the ANR circuit  2000  back into stable operation and/or back to safe acoustic output levels in response to an out-of-bound condition being detected. 
         [0141]    As will be familiar to those skilled in the art of controlling digital signal processing for audio signals, it is often necessary to coordinate the updating of various audio processing settings to occur during intervals between the processing of pieces of audio data, and it is often necessary to cause the updating of at least some of those settings to be made during the same interval. Failing to do so can result in the incomplete programming of filter coefficients, an incomplete or malformed definition of a transfer function, or other mismatched configuration issue that can result in undesirable sounds being created and ultimately acoustically output, including and not limited to, sudden popping or booming noises that can surprise or frighten a listener, sudden increases in volume that are unpleasant and can be harmful to a listener, or howling feedback sounds in the case of updating feedback-based ANR settings that can also be harmful. 
         [0142]    In some implementations, the buffers  620   a - c  of any of  FIGS. 6   a - c  are dedicated hardware-implemented registers, the contents of which are able to be clocked into registers within the VGAs, the digital filters, the summing nodes, the clocks of the clock bank  570  (if present), switch array  540  (if present), the DMA device  541  (if present) and/or other components. In other implementations, the buffers  620   a - c  of  FIGS. 6   a - c  are assigned locations within the storage  520 , the contents of which are able to be retrieved by the processing device  510  and written by the processing device  510  into other locations within the storage  520  associated with instantiations of the VGAs, digital filters, and summing nodes, and/or written by the processing device  510  into registers within the clocks of the clock bank  570  (if present), the switch array  540  (if present), the DMA device  541  (if present) and/or other components. 
         [0143]      FIG. 6   a  depicts the triple-buffering of VGA settings, including gain values, employing variants of the buffers  620   a - c  that each store differing ones of VGA settings  626 . An example of a use of such triple-buffering of VGA gain values may be the compression controller  950  operating one or more VGAs to reduce the amplitude of sounds represented by digital data in response to detecting occurrences and/or indications of impending occurrences of clipping and/or other audible artifacts in the acoustic output of the acoustic driver  190 . In some implementations, the compression controller  950  stores new VGA settings into a selected one of the buffers  620   a  and  620   b.  At a subsequent time that is synchronized to the flow of pieces of digital data through one or more of the VGAs, the settings stored in the selected one of the buffers  620   a  and  620   b  are provided to those VGAs, thereby avoiding the generation of audible artifacts. As those skilled in the art will readily recognize, the compression controller  950  may repeatedly update the gain settings of VGAs over a period of time to “ramp down” the amplitude of one or more sounds to a desired level of amplitude, rather than to immediately reduce the amplitude to that desired level. In such a situation, the compression controller  950  would alternate between storing updated gain settings to the buffer  620   a  and storing updated gain settings to the buffer  620   b,  thereby enabling the decoupling of the times at which each of the buffers  620   a  and  620   b  are each written to by the compression controller  950  and the times at which each of the buffers provide their stored VGA settings to the VGAs. However, a set of more conservatively selected VGA settings is stored in the buffer  620   c,  and these failsafe settings may be provided to the VGAs in response to an out-of-bound condition being detected. Such provision of the VGA settings stored in the buffer  620   c  overrides the provision of any VGA settings stored in either of the buffers  620   a  and  620   b.    
         [0144]      FIG. 6   b  depicts the triple-buffering of filter settings, including filter coefficients, employing variants of the buffers  620   a - c  that each store differing ones of filter settings  625 . An example of a use of such triple-buffering of filter coefficients may be adjusting the range of frequencies and/or the degree of attenuation of noise sounds that are reduced in the feedback-based ANR provided by the personal ANR device  1000 . In some implementations, processing device  510  is caused by the ANR routine  525  to store new filter coefficients into a selected one of the buffers  620   a  and  620   b.  At a subsequent time that is synchronized to the flow of pieces of digital data through one or more of the digital filters, the settings stored in the selected one of the buffers  620   a  and  620   b  are provided to those digital filters, thereby avoiding the generation of audible artifacts. Another example of a use of such triple-buffering of filter coefficients may be adjusting the crossover frequency employed by the digital filters within the filter block  450  in some of the above signal processing topologies to divide the sounds of the modified pass-through audio into lower and higher frequency sounds. At a time synchronized to at least the flow of pieces of digital data associated with pass-through audio through the digital filters of the filter block  450 , filter settings stored in one or the other of the buffers  620   a  and  620   b  are provided to at least some of the digital filters. 
         [0145]      FIG. 6   c  depicts the triple-buffering of either all or a selectable subset of clock, VGA, filter and topology settings, employing variants of the buffers  620   a - c  that each store differing ones of topology settings  622 , filter settings  625 , VGA settings  626  and clock settings  627 . An example of a use of triple-buffering of all of these settings may be changing from one signal processing topology to another in response to a user of the personal ANR device  1000  operating a control to activate a “talk-through” feature in which the ANR provided by the personal ANR device  1000  is altered to enable the user to more easily hear the voice of another person without having to remove the personal ANR device  1000  or completely turn off the ANR function. The processing device  510  may be caused to store the settings required to specify a new signal processing topology in which voice sounds are more readily able to pass to the acoustic driver  190  from the feedforward microphone  130 , and the various settings of the VGAs, digital filters, data clocks and/or other components of the new signal processing topology within one or the other of the buffers  620   a  and  620   b.  Then, at a time synchronized to the flow of at least some pieces of digital data representing sounds through at least one component (e.g., an ADC, a VGA, a digital filter, a summing node, or a DAC), the settings are used to create the interconnections for the new signal processing topology (by being provided to the switch array  540 , if present) and are provided to the components that are to be used in the new signal processing topology. 
         [0146]    However, some variants of the triple-buffering depicted in  FIG. 6   c  may further incorporate a mask  640  providing the ability to determine which settings are actually updated as either of the buffers  620   a  and  620   b  provide their stored contents to one or more components. In some embodiments, bit locations within the mask are selectively set to either 1 or 0 to selectively enable the contents of different ones of the settings corresponding to each of the bit locations to be provided to one or more components when the contents of one or the other of the buffers  620   a  and  620   b  are to provide updated settings to the components. The granularity of the mask  640  may be such that each individual setting may be selectively enabled for updating, or may be such that the entirety of each of the topology settings  622 , the filter settings  625 , the VGA setting  626  and the clock setting  627  are able to be selected for updating through the topology settings mask  642 , the filter settings mask  645 , the VGA settings mask  646  and the clock settings mask  647 , respectively. 
         [0147]      FIGS. 7   a  and  7   b  each depict variations of a number of possible additions to the internal architectures  2200   a  and  2200   b,  respectively, of the ANR circuit  2000 . Therefore, it should be noted that for sake of simplicity of discussion, only portions of the internal architectures  2200   a  and  2200   b  associated with these possible additions are depicted. Some of these possible additions rely on the use of the interface  530  coupling the ANR circuit  2000  to other devices via at least one bus  535 . Others of these possible additions rely on the use of the interface  530  to receive a signal from at least one manually-operable control. 
         [0148]    More particularly, in executing a sequence of instructions of the loading routine  522  to possibly retrieve at least some of the contents of the ANR settings  527  from an external storage device (e.g., the storage device  170 ), the processing device  510  may be caused to configure the ANR circuit  2000  to accept those contents from an external processing device  9100 , instead. Also, to better enable the use of adaptive algorithms in providing feedback-based and/or feedforward-based ANR functions, the external processing device  9100  may be coupled to the ANR circuit  2000  to augment the functionality of the ANR circuit  2000  with analysis of statistical information concerning feedback reference sounds, feedforward reference sounds and/or pass-through audio, where side-chain information is provided from downsampling and/or other filters either built into or otherwise connected to one or more of the ADCs  210 ,  310  and  410 . Further, to enable cooperation between two of the ANR circuits  2000  to achieve a form of binaural feedforward-based ANR, each one of the ANR circuits  2000  may transmit copies of feedforward reference data to the other. Still further, one or more of the ANR circuit  2000  and/or the external processing device  9100  may monitor a manually-operable talk-through control  9300  for instances of being manually operated by a user to make use of a talk-through function. 
         [0149]    The ANR circuit  2000  may accept an input from the talk-through control  9300  coupled to the ANR circuit  2000  directly, through another ANR circuit  2000  (if present), or through the external processing device  9100  (if present). Where the personal ANR device  1000  incorporates two of the ANR circuit  2000 , the talk-through control  9300  may be directly coupled to the interface  530  of each one of the ANR circuit  2000 , or may be coupled to a single one of the external processing device  9100  (if present) that is coupled to both of the ANR circuits  2000 , or may be coupled to a pair of the external processing devices  9100  (if present) where each one of the processing devices  9100  is separately coupled to a separate one of each of the ANR circuits  2000 . 
         [0150]    Regardless of the exact manner in which the talk-through control  9300  is coupled to other component(s), upon the talk-through control  9300  being detected as having been manually operated, the provision of at least feedforward-based ANR is altered such that attenuation of sounds in the human speech band detected by the feedforward microphone  130  is reduced. In this way, sounds in the human speech band detected by the feedforward microphone  130  are actually conveyed through at least a pathway for digital data associated with feedforward-based ANR to be acoustically output by the acoustic driver  190 , while other sounds detected by the feedforward microphone  130  continue to be attenuated through feedforward-based ANR. In this way, a user of the personal ANR device  1000  is still able to have the benefits of at least some degree of feedforward-based ANR to counter environmental noise sounds, while also being able to hear the voice of someone talking nearby. 
         [0151]    As will be familiar to those skilled in the art, there is some variation in what range of frequencies is generally accepted as defining the human speech band from ranges as wide as 300 Hz to 4 KHz to ranges as narrow as 1 KHz to 3 KHz. In some implementations, the processing device  510  and/or the external processing device  9100  (if present) is caused to respond to the user operating the talk-through control  9300  by altering ANR settings for at least the filters in the pathway for feedforward-based ANR to reduce the range of frequencies of environmental noise sounds attenuated through feedforward-based ANR such that the feedforward-based ANR function is substantially restricted to attenuating frequencies below whatever range of frequencies is selected to define the human speech band for the personal ANR device  1000 . Alternatively, the ANR settings for at least those filters are altered to create a “notch” for a form of the human speech band amidst the range of frequencies of environmental noise sounds attenuated by feedforward-based ANR, such that feedforward-based ANR attenuates environmental noise sounds occurring in frequencies below that human speech band and above that human speech band to a considerably greater degree than sounds detected by the feedforward microphone  130  that are within that human speech band. Either way, at least one or more filter coefficients are altered to reduce attenuation of sounds in the human speech band. Further, the quantity and/or types of filters employed in the pathway for feedforward-based ANR may be altered, and/or the pathway for feedforward-based ANR itself may be altered. 
         [0152]    Although not specifically depicted, an alternative approach to providing a form of talk-through function that is more amenable to the use of analog filters would be to implement a pair of parallel sets of analog filters that are each able to support the provision of feedforward-based ANR functionality, and to provide a form of manually-operable talk-through control that causes one or more analog signals representing feedforward-based ANR to be routed to and/or from one or the other of the parallel sets of analog filters. One of the parallel sets of analog filters is configured to provide feedforward-based ANR without accommodating talk-through functionality, while the other of the parallel sets of filters is configured to provide feedforward-based ANR in which sounds within a form of the human speech band are attenuated to a lesser degree. Something of a similar approach could be implemented within the internal architecture  2200   a  as yet another alternative, in which a form of manually-operable talk-through control directly operates at least some of the switching devices within the switch array  540  to switch the flow of digital data between two parallel sets of digital filters. 
         [0153]      FIG. 8  is a flowchart of an implementation of a possible loading sequence by which at least some of the contents of the ANR settings  527  to be stored in the storage  520  may be provided across the bus  535  from either the external storage device  170  or the processing device  9100 . This loading sequence is intended to allow the ANR circuit  2000  to be flexible enough to accommodate any of a variety of scenarios without alteration, including and not limited to, only one of the storage device  170  and the processing device  9100  being present on the bus  535 , and one or the other of the storage device  170  and the processing device  9100  not providing such contents despite both of them being present on the bus. The bus  535  may be either a serial or parallel digital electronic bus, and different devices coupled to the bus  535  may serve as a bus master at least coordinating data transfers. 
         [0154]    Upon being powered up and/or reset, the processing device  510  accesses the storage  520  to retrieve and execute a sequence of instructions of the loading routine  522 . Upon executing the sequence of instructions, at  632 , the processing device  510  is caused to operate the interface  530  to cause the ANR circuit  2000  to enter master mode in which the ANR circuit  2000  becomes a bus master on the bus  535 , and then the processing device  510  further operates the interface  530  to attempt to retrieve data (such as part of the contents of the ANR settings  527 ) from a storage device also coupled to the bus  535 , such as the storage device  170 . If, at  633 , the attempt to retrieve data from a storage device succeeds, then the processing device  510  is caused to operate the interface  530  to cause the ANR circuit  2000  to enter a slave mode on the bus  535  to enable another processing device on the bus  535  (such as the processing device  9100 ) to transmit data to the ANR circuit  2000  (including at least part of the contents of the ANR settings  527 ) at  634 . 
         [0155]    However, if at  633 , the attempt to retrieve data from a storage device fails, then the processing device  510  is caused to operate the interface  530  to cause the ANR circuit  2000  to enter a slave mode on the bus  535  to enable receipt of data from an external processing device (such as the external processing device  9100 ) at  635 . At  636 , the processing device  510  is further caused to await the receipt of such data from another processing device for a selected period of time. If, at  637 , such data is received from another processing device, then the processing device  510  is caused to operate the interface  530  to cause the ANR circuit  2000  to remain in a slave mode on the bus  535  to enable the other processing device on the bus  535  to transmit further data to the ANR circuit  2000  at  638 . However, if at  637 , no such data is received from another processing device, then the processing device  510  is caused to operate the interface  530  to cause the ANR circuit  2000  to return to being a bus master on the bus  535  and to again attempt to retrieve such data from a storage device at  632 . 
         [0156]      FIGS. 9   a  and  9   b  each depict a manner in which either of the internal architectures  2200   a  and  2200   b  may support the provision of side-chain data to the external processing device  9100 , possibly to enable the processing device  9100  to add adaptive features to feedback-based and/or feedforward-based ANR functions performed by the ANR circuit  2000 . In essence, while the ANR circuit  2000  performs the filtering and other aspects of deriving feedback and feedforward anti-noise sounds, as well as combining those anti-noise sounds with pass-through audio, the processing device  9100  performs analyses of various characteristics of feedback and/or feedforward reference sounds detected by the microphones  120  and/or  130 . Where the processing device  9100  determines that there is a need to alter the signal processing topology of the ANR circuit  2000  (including altering a filter block topology of one of the filter blocks  250 ,  350  and  450 ), alter VGA gain values, alter filter coefficients, alter clock timings by which data is transferred, etc., the processing device  9100  provides new ANR settings to the ANR circuit  2000  via the bus  535 . As previously discussed, those new ANR settings may be stored in one or the other of the buffers  620   a  and  620   b  in preparation for those new ANR settings to be provided to components within the ANR circuit  2000  with a timing synchronized to one or more data transfer rates at which pieces of digital data representing sounds are conveyed between components within the ANR circuit  2000 . Indeed, in this way, the provision of ANR by the ANR circuit  2000  can also be made adaptive. 
         [0157]    In supporting such cooperation between the ANR circuit  2000  and the external processing device  9100 , it may be deemed desirable to provide copies of the feedback reference data, the feedforward reference data and/or the pass-through audio data to the processing device  9100  without modification. However, it is contemplated that such data may be sampled at high clock frequencies, possibly on the order of 1 MHz for each of the feedback reference data, the feedforward reference data and the pass-through audio data. Thus, providing copies of all of such data at such high sampling rates through the bus  535  to the processing device  9100  may place undesirably high burdens on the ANR circuit  2000 , as well as undesirably increase the power consumption requirements of the ANR circuit  2000 . Further, at least some of the processing that may be performed by the processing device  9100  as part of such cooperation with the ANR circuit  2000  may not require access to such complete copies of such data. Therefore, implementations of the ANR circuit  2000  employing either of the internal architectures  2200   a  and  2200   b  may support the provision of lower speed side-chain data made up of such data at lower sampling rates and/or various metrics concerning such data to the processing device  9100 . 
         [0158]      FIG. 9   a  depicts an example variant of the ADC  310  having the ability to output both feedforward reference data representative of the feedforward reference analog signal received by the ADC  310  from the feedforward microphone  130  and corresponding side-chain data. This variant of the ADC  310  incorporates a sigma-delta block  322 , a primary downsampling block  323 , a secondary downsampling block  325 , a bandpass filter  326  and a RMS block  327 . The sigma-delta block  322  performs at least a portion of a typical sigma-delta analog-to-digital conversion of the analog signal received by the ADC  310 , and provides the feedforward reference data at a relatively high sampling rate to the primary downsampling block  323 . The primary downsampling block  323  employs any of a variety of possible downsampling (and/or decimation) algorithms to derive a variant of the feedforward reference data at a more desirable sampling rate to whatever combination of VGAs, digital filters and/or summing nodes is employed in deriving feedforward anti-noise data representing anti-noise sounds to be acoustically output by the acoustic driver  190 . However, the primary downsampling block  323  also provides a copy of the feedforward reference data to the secondary downsampling block  325  to derive a further downsampled (and/or decimated) variant of the feedforward reference data. The secondary downsampling block  325  then provides the further downsampled variant of the feedforward reference data to the bandpass filter  326  where a subset of the sounds represented by the further downsampled feedforward reference data that are within a selected range of frequencies are allowed to be passed on to the RMS block  327 . The RMS block  327  calculates RMS values of the further downsampled feedforward reference data within the selected range of frequencies of the bandpass filter  326 , and then provides those RMS values to the interface  530  for transmission via the bus  535  to the processing device  9100 . 
         [0159]    It should be noted that although the above example involved the ADC  310  and digital data associated with the provision of feedforward-based ANR, similar variations of either of the ADCs  210  and  410  involving either of the feedback-based ANR and pass-through audio, respectively, are possible. Also possible are alternate variations of the ADC  310  (or of either of the ADCs  210  and  410 ) that do not incorporate the secondary downsampling block  325  such that further downsampling (and/or decimating) is not performed before data is provided to the bandpass filter  326 , alternate variations that employ an A-weighted or B-weighted filter in place of or in addition to the bandpass filter  326 , alternate variations that replace the RMS block  327  with another block performing a different form of signal strength calculation (e.g., an absolute value calculation), and alternate variations not incorporating the bandpass filter  326  and/or the RMS block  327  such that the downsampled (and/or decimated) output of the secondary downsampling block  325  is more conveyed to the interface with less or substantially no modification. 
         [0160]      FIG. 9   b  depicts an example variant of the filter block  350  having the ability to output both feedforward anti-noise data and side-chain data corresponding to the feedforward reference data received by the filter block  350 . As has been previously discussed at length, the quantity, type and interconnections of filters within the filter blocks  250 ,  350  and  450  (i.e., their filter block topologies) are each able to be dynamically selected as part of the dynamic configuration capabilities of either of the internal architectures  2200   a  and  2200   b.  Therefore, this variant of the filter block  350  may be configured with any of a variety of possible filter block topologies in which both of the functions of deriving feedforward anti-noise data and side-chain data are performed. 
         [0161]      FIGS. 10   a  and  10   b  each depict a manner in which either of the internal architectures  2200   a  and  2200   b  may support binaural feedforward-based ANR in which feedforward reference data is shared between a pair of the ANR circuits  2000  (with each incarnation of the ANR circuit  2000  providing feedforward-based ANR to a separate one of a pair of the earpieces  100 ). In some implementations of the personal ANR device  1000  having a pair of the earpieces  100 , feedforward reference data representing sounds detected by separate feedforward microphones  130  associated with each of the earpieces  100  is provided to both of the separate ANR circuits  2000  associated with each of the earpieces. This is accomplished through an exchange of feedforward reference data across a bus connecting the pair of ANR circuits  2000 . 
         [0162]      FIG. 10   a  depicts an example addition to a signal processing topology (perhaps, any one of the signal processing topologies previously presented in detail) that includes a variant of the filter block  350  having the ability to accept the input of feedforward reference data from two different feedforward microphones  130 . More specifically, the filter block  350  is coupled to the ADC  310  to more directly receive feedforward reference data from the feedforward microphone  130  that is associated with the same one of the earpieces to which the one of the ANR circuits  2000  in which the filter block  350  resides is also associated. This coupling between the ADC  310  and the filter block  350  is made in one of the ways previously discussed with regard to the internal architectures  2200   a  and  2200   b.  However, the filter block  350  is also coupled to the interface  530  to receive other feedforward reference data from the feedforward microphone  130  that is associated with the other of the earpieces  100  through the interface  530  from the ANR circuit  2000  that is also associated with the other of the earpieces  100 . Correspondingly, the output of the ADC  310  by which feedforward reference data is provided to the filter block  350  is also coupled to the interface  530  to transmit its feedforward reference data to the ANR circuit  2000  associated with the other one of the earpieces  100  through the interface  530 . The ANR circuit  2000  associated with the other one of the earpieces  100  employs this same addition to its signal processing topology with the same variant of its filter block  350 , and these two incarnations of the ANR circuit  2000  exchange feedforward reference data through their respective ones of the interface  530  across the bus  535  to which both incarnations of the ANR circuit  2000  are coupled. 
         [0163]      FIG. 10   b  depicts another example addition to a signal processing topology that includes a variant of the filter block  350 . However, this variant of the filter block  350  is involved in the transmission of feedforward reference data to the ANR circuit  2000  associated with the other one of the earpieces  100 , in addition to being involved in the reception of feedforward reference data from that other incarnation of the ANR circuit  2000 . Such additional functionality may be incorporated into the filter block  350  in implementations in which it is desired to in some way filter or otherwise process feedforward reference data before it is transmitted to the other incarnation of the ANR circuit  2000 . 
         [0164]    Other implementations are within the scope of the following claims and other claims to which the applicant may be entitled.
At initialization of an ANR circuit (i.e., at so-called boot time), attempts are made to alternately obtain ANR settings from an external storage device by operating the ANR circuit as a master of a bus and from an external processing device by operating the ANR circuit as a slave of the bus. Such alternating attempts may be repeated until the ANR settings are loaded.