BACKGROUND 
       [0001]    Drivers are increasingly required to interact with electrically transmitted audible signals, particularly speech, such as with a mobile telephone or with systems for navigation, information, and entertainment. 
         [0002]    It would be beneficial if the interactive audible signals were to sound as coming from a source in front of the driver, rather than from the side or rear. In this manner, it would feel more natural for the driver to interactively respond by speaking in a forward direction toward the perceived source of the audible signals, without turning the head. In most vehicles, however, there is no provision for locating a loudspeaker in front of the driver—audible signals must physically originate from loudspeakers in other locations. It is desirable, therefore, to have a method for electronically altering the signals prior to input to the loudspeakers in order to simulate a virtual sound source in front of the driver, taking into account the location of the driver&#39;s head and the acoustical characteristics of the vehicle&#39;s interior. This goal is met by the present invention. 
       SUMMARY 
       [0003]    According to an embodiment of the present invention, a method is provided for creating a virtual audible source for an audible signal at a virtual source location relative to a listener seated in a seat of a vehicle interior, the vehicle interior having interior acoustical characteristics and at least one loudspeaker having a predetermined loudspeaker location, the method including: obtaining seat data from one or more sensors located in the seat; computing an estimated head position of the listener based on the seat data; computing an acoustical transfer function for the at least one loudspeaker according to the estimated head position, the virtual source location, the predetermined loudspeaker location, and the interior acoustical characteristics; applying the acoustical transfer function to the audible signal to obtain a filtered audible signal; and sending the filtered audible signal to the at least one loudspeaker. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0004]    Examples are described in the following detailed description and illustrated in the accompanying drawings in which: 
           [0005]      FIG. 1  conceptually illustrates a vehicle interior as seen by a driver. 
           [0006]      FIG. 2  conceptually illustrates a side view of a vehicle interior showing the driver sitting on an adjustable seat with position and pressure sensors. 
           [0007]      FIG. 3  illustrates a method according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    The term “vehicle” herein encompasses all means of transportation for passengers and freight, non-limiting examples of which include: aircraft, trains, boats, and road vehicles. Embodiments of the invention are described in terms of a vehicle driver, but the invention is also applicable to any listener in a vehicle. 
         [0009]    The term “head-up display” (HUD) herein denotes any transparent display that presents visual data to a user from a direction along the user&#39;s normal line-of-sight, so that the user need not turn the head or eyes away from the normal line-of-sight to view the display. As used herein, HUD also relates in particular to a display projected onto the inside surface of a vehicle windshield and reflected toward the user therefrom. 
         [0010]    Sources of audible signals in a vehicle include loudspeakers within the vehicle interior. 
         [0011]      FIG. 1  conceptually illustrates a vehicle interior  100  as seen by a driver. A virtual audible signal source  101  according to embodiments of the invention is in front of the driver, as the driver looks through a windshield  103 . A first loudspeaker  107  and a second loudspeaker  109  are the physical sources of the audible signal. 
         [0012]    In the field of acoustics, a head-related transfer function (HRTF) characterizes how an ear receives a sound from a point in space. It is known that a pair of HRTFs for the listener&#39;s ears can be used to synthesize a binaural sound that appears to the listener to originate from a specified point. Therefore, according to embodiments of the invention, a pair of HRTFs are used to calculate a transfer function by which an audible signal can be processed to produce physical audible signals emanating from loudspeaker  107  and loudspeaker  109  which combine to synthesize an audible signal that sounds to the driver as if the audible signal originates from virtual audible signal source  101 . 
         [0013]    In order to synthesize an audible signal having virtual audible signal source  101 , it is necessary to derive the applicable HRTFs for the position and characteristics of the listener&#39;s head. 
         [0014]    According to embodiments of the invention, HRTF&#39;s may be approximated utilizing the following data:
       listener head position estimated according to data obtained from a vehicle seat;   a generic HRTF;   a vehicle-specific transfer function that relates to the acoustics and geometry of a specific vehicle model interior;   a predetermined loudspeaker position; and   a predetermined virtual source position.       
 
       Estimating Listener Head Position 
       [0020]      FIG. 2  conceptually illustrates a driver  201  in vehicle interior  100 . A driver  201  is seated on a seat which includes: a lower cushion  203  which attached to a vehicle floor  205 ; a back  207  attached to lower cushion  203 , and a headrest  209  attached to back  207 . Typically, all of the foregoing components may be adjusted according to the preferences of driver  201 : lower cushion  203  typically can be raised, lowered, angled, and adjusted forwards or backwards; back  207  typically can be adjusted forward and backwards; and headrest  209  typically can be raised and lowered. 
         [0021]    According to embodiments of the invention, the seat components are provided with sensors to report their respective adjustment positions: seat cushion  203  has an adjustment position sensor  215 ; back  207  has an adjustment position sensor  213 ; and headrest  209  has an adjustment position sensor  211 . In addition, an adjustment position sensor  217  reports the adjustment position of a steering wheel  235 . 
         [0022]    Also, according to embodiments of the invention, the actual seating position of driver  201  is reported by contact pressure sensors in the seat components: seat cushion  203  contains pressure sensors such as contact pressure sensors  229  and  231 ; back  207  contains pressure sensors such as contact pressure sensors  223 ,  225 , and  227 ; and headrest  209  contains a contact pressure sensor  221 . These sensors detect the presence of the driver in the seat and, together with the adjustment position sensors, provide data for computing an estimated position of the driver&#39;s head. 
         [0023]    According to embodiments of the invention, anthropometric data is used for computing the estimated position of the driver&#39;s head. 
         [0024]    In a further embodiment of the invention, a digital camera  219  provides supplementary head position data, when lighting conditions permit. In an additional embodiment, infrared lighting is used under low-light conditions. Visual data from camera  219  may refine the estimate of the driver&#39;s head position. 
         [0025]    Based on the estimated driver&#39;s head position, one or more transfer functions are computed, by which sounds emanating from loudspeakers  107  and  109  ( FIG. 1 ) can be made to simulate binaural audible signals that sound to driver  201  as originating from virtual audible source  103 . 
         [0026]    As indicated previously, according to embodiments of the invention, the HRTF may be decomposed into the generic HRTF and the vehicle-specific transfer function. 
         [0027]    In a particular embodiment, the generic HRTF provides data for a surface of a sphere centered around the mid position between the driver&#39;s ears. In a non-limiting example, the sphere has a radius of 50 cm. The vector for the loudspeaker transfer function thus involves the generic HRTF with added vehicle-related components. In this manner, HRTF tables may be acquired or measured offline, and a single generic table can be used for a large number of vehicle models. 
         [0028]    In additional embodiments of the invention, the transfer functions may be computed once per vehicle model, for a geometrical grid covering potential driver head positions. In a non-limiting example, 500 grid points may be used. The number of grid points may vary according to the method used to estimate driver head position. 
         [0029]    A possible location for the virtual sound source is a HUD in front of the driver projected on the windshield. The projected HUD image may be related to the audible signal; live video, static images, icons, avatars, maps, and the like may be used where applicable. 
       Method and Implementation 
       [0030]      FIG. 3  illustrates a method according to an embodiment of the invention. In a step  301 , seat data  303  related to the sitting position of driver  201  ( FIG. 2 ) is obtained from sensors, such as sensors illustrated in  FIG. 2 . In a step  305 , an estimated head position  309  of driver  201  is computed, based on seat data  303  and anthropometric data  307 . 
         [0031]    In a step  311 , an acoustical transfer function  329  is computed, based on estimated head position  309 , a virtual source location  313 , a loudspeaker location  315 , and a head-related transfer function (HRTF)  319 . According to embodiments of the invention, HRTF  319  is composed of a generic HRTF  321  and a custom vehicle-dependent transfer function  323 , which is computed specifically for the particular model of vehicle under consideration. 
         [0032]    In an embodiment of the invention, step  311  is performed off-line once per vehicle model, for a predetermined set of grid points  328  covering a region in space where the driver&#39;s head will be. 
         [0033]    In an embodiment of the invention, step  311  includes the use of a transfer function matrix from two loudspeakers to the ears such that a sound of one loudspeaker is perceived at one ear, cancelling the sound from the other loudspeaker at that ear, and transfer functions from the ears to a virtual source location. 
         [0034]    In a step  327  acoustical transfer function  329  is applied to an audible signal  325  to yield a filtered audible signal  331 , and in a step  333 , filtered audible signal  331  is sent to loudspeaker  107  ( FIG. 1 ). In an embodiment of the invention, steps  327  and  333  are performed repeatedly in real time. The driver&#39;s head position is estimated, as in steps  301  and  305 , then the nearest grid point (of grid points  328 ) to the driver&#39;s head is found, and then transfer function  329  is retrieved for that grid point. 
         [0035]    A further embodiment of the present invention provides a computer product for performing the foregoing method, or variants thereof. 
         [0036]    A computer product according to this embodiment includes a set of executable commands for performing the method on a computer, wherein the executable commands are contained within a tangible computer-readable non-transient data storage medium including, but not limited to: computer media such as magnetic media and optical media; computer memory; semiconductor memory storage; flash memory storage; data storage devices and hardware components; such that when the executable commands of the computer product are executed, the computer product causes the computer to perform the method. 
         [0037]    In this embodiment, a “computer” is any data processing apparatus for executing a set of executable commands to perform the method, in particular, an on-board computer in the vehicle, such as an on-board computer  241  ( FIG. 2 ), which contains a sound-processing interface with audio amplifiers, audio filters, and appropriate software as necessary to handle all manner of audible signals, including, but not limited to: interactive dialogue, telephone conversations, navigational instructions, and so forth.
A method for providing audible signals (such as speech) to a driver of a vehicle which appear to originate from a virtual sound source in front of the driver, so that it will feel normal for the driver to respond interactively by speaking without turning the head to the source of the audible signal. The driver's head position is estimated according to data provided by sensors in the driver's seat, and this position data, together with acoustical characteristics of the vehicle interior, is used to derive a transfer function for filtering electrical audible signals to the loudspeakers to simulate a virtual sound source in front of the driver.