[sdiy] Digital Noise, FYI

[David G. Dixon]

> If you replace that CPLD *thing* with an analog one FET based S/H
> and one NPN based noise source you end up with a cheaper and
> simpler and better sounding result.

Possibly, but it depends on finding a transistor with a significant amount
of thermal noise (they don't all have it).  Also, you might find that you
are picking up local radio stations on the unconnected collector pin (yes,
even if you cut it off), which you can hear quite clearly when you amplify
the noise signal a million times or so.  While this might be cool in its own
right, it probably isn't what you want from a noise source.

With the digital noise source, you have a couple of different options for
how to harvest the noise.  You can feed some or all of the random word to a
DAC, which gives "square noise" which you can then filter to make less
square if desired, or you can feed the random output bit to an integrator
(with an input capacitor to prevent the integrator from hitting the rails).
You can even do both simultaneously.