used to. Dolby tried to get around this by introducing a version of their own called CCIR-Dolby which incorporated a 62 dB shift into the result (and a cheaper average reading rectifier), but this only confused matters, and was very much disapproved of by the CCIR. With the demise of the CCIR, the 468 standard is now maintained as ITU-R 468, by the International Telecommunication Union, and forms part of many national and international standards, in particular by the IEC (International Electrotechnical Commission), and the BSI (British Standards Institute). It is the only way to measure noise that allows fair comparisons; and yet the flawed A-weighting has made a comeback in the consumer field recently, for the simple reason that it gives the lower figures that are considered more impressive by marketing departments. Signal-to-noise ratio and dynamic range Audio equipment specifications tend to include the terms signal-to-noise ratio and dynamic range, both of which have multiple definitions, sometimes treated as synonyms. The exact meaning must be specified along with the measurement. Analog Dynamic range used to mean the difference between maximum level and noise level, with maximum level defined as a clipping signal with a specified THD+N. The term has become corrupted by a tendency to refer to the dynamic range of CD players as meaning the noise level on a blank recording with no dither, (in other words, just the analog noise content at the output). This is not particularly useful; especially since many CD players incorporate automatic muting in the absence of signal. Since the early 1990s various writers such as Julian Dunn have suggested that dynamic range be measured in the presence of a low-level test signal. Thus, any spurious signals caused by the test signal or distortion will not degrade the signal-to-noise ratio. This also addresses concerns about muting circuits. Digital In 1999, Steven Harris & Clif Sanchez Cirrus Logic published a white paper titled "Personal Computer Audio Quality Measurements" stating: In 2000 the AES released AES Information Document 6id-2000 which defined dynamic range as "20 times the logarithm of the ratio of the full-scale signal to the r.m.s. noise floor in the presence of signal, expressed in dB2 FS" with the following note: See also Audio quality measurement Noise Sound level meter ITU-R 468 noise weighting Noise measurement Headroom Weighting filter Equal-loudness contour Fletcher–Munson curves References External links Noise measurement briefing Audio electronics Broadcast engineering