[sdiy] Information Reduction in Digital media

[Grant Richter]

After reading the Rupert Neve interview in "Tape-Op" magazine, I really
started to research the basic information content of analog signals.

My experiments with 24 bit converters and Spectra-Lab software have shown
that even a fairly crappy analog design running from +/- 15 volts
(breadboard), has an unmeasurable signal to noise ratio at 24 bits.

In other words, even simple analog really does run at a much better
information content than even a good 24 bit A/D converter can resolve.

For reference, Claude Shannon's original 1948 paper on the mathematics of
communication can be accessed at:

http://cm.bell-labs.com/cm/ms/what/shannonday/shannon1948.pdf

It is interesting to note that Mr. Shannon never realized his work would be
interpreted as broadly as it has been.

Some information scientists seem to think that Boltzman's constant sets a
basic limit on the thermal representation of information content. The
Boltzman constant is defined by Joules per Kelvin, and a Joule is just a
Watt-Second by another name. Also the audio 0 dB point is specified as 1
milliwatt into 600 ohms.

Doing fast sloppy math, a 1 milliwatt-second source has a thermally limited
information content (at room temperature 300 deg Kelvin) of something like
2^64 bits per second.

This is WAY better than the 2^32 bits per second used by the best digital
media (remember, half of 2^64 is 0.5 x 2^64 NOT 2^32).

So the general feeling that analog audio sources are cognitively different
than digital sources would seem to be supported by these ideas from physics
and mathematics.