[sdiy] VC variable bit-rate audio digitizer? help!

[Grant Richter]

>> So obviously there are various known ways to do plain bit rate
>> conversion. A much more interesting module, in my opinion, would be
>> one that could vary the amplitude quantization _linearly_ from 2
>> states to some hi-fi number of states. Is THAT feasible?

The process of limiting a continuous function to certain levels is called
quantization. The process produces quantization noise, which is reduced by
6 dB for each additional bit. So 8 bit digitization has a signal to noise
ratio of 48 dB (8 x 6dB) and 16 bit audio has a signal to noise ratio of 96
dB (16 x 6 dB).

A sine wave recorded on a 16 bit system at -48 dB is only going to be
digitized to 8 bits. This is where the quantization noise is most apparent,
at the tail end of decays and the like. People have become very sensitized
to quantization noise (sizzle) and complain about being able to hear it in
12 bit systems like the early DX7s.

You can control the quantization by recording at various low levels, and
then do digital gain increase back to 0 dB, which is a multiplication
without removing the quantization noise introduce by the low level
recording.