[sdiy] Information Reduction in Digital media

[Grant Richter]

> Grant wrote:
>> 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.
> 
> Wow! I want your crappy power supply and breadboard that has a noise
> floor of better than -144dB.

Believe me, no one was more surprised than myself.

To clarify, using a real time spectrum analyzer with an M-Audio Delta 66
card, the general noise floor is at -120 dB relative to +4 dB. This is with
a shorted input.

The broad spectrum noise floor appear as a fluctuating horizontal line.

Using this method, you can differentiate between noise signals appearing at
certain frequencies and broadband noise. So while there is an obvious spike
at 60 Hz and it harmonics, the general noise floor remains at the A/D level.

To me, this indicates that he white noise content is equal to or less than
the self noise of the audio card.