mike@asgb.UUCP (10/31/84)
In reference to the 8 bit logarithmic representation described by Richard Schooler (inmet!schooler): he suggested an 8 bit representation with a sign bit and a seven bit fixed point exponent with three fraction bits. This gives a dynamic range of 2^(+-(15+7/8)) or 96 dB and "an absolute S/N of 93 dB, and an instantaneous S/N (precision, roughly) of 32 dB." This representation does not however, consider waveform fidelity. At each sampling point, the signal must be quantized to one of the values represented by the encoding scheme. In the 8 bit scheme, each quantum level is greater than the previous by a factor of 1.09. A 9% jump between levels and a maximum quantizing error of 4.5%. This error due to the lack of precision does not yield a greater S/N, it's DISTORTION. True, filtering techniques can minimize the distortion, but 4.5% isn't quite a high fidelity source to begin with. This encoding does have the interesting characteristic that the difference between quantizing levels is a constant factor. In the current CDs 16 bit encoding, the error varies from 50% (!) between 0 and 1 to .00075% between 65534 and 65535. If a 16 bit logarithmic representation was used, the error would be a constant .024%. I don't know if this is a significant characteristic, but it at least has a nice consistency to it. Mike Rosenlof ...hplabs!sdcrdcf!\ -bmcg!asgb!mike ...allegra!sdcsvax!/ Burroughs Advanced Systems Group Boulder, Colorado