[sdiy] Vote for your favorite noise source

[Magnus Danielson]

From: jorgen.bergfors at idg.se
Subject: Re: [sdiy] Vote for your favorite noise source
Date: Mon, 13 May 2002 15:54:23 +0200

> 
> >If used for a source of random, I have not seen a difference.
> 
> Well, I have. Actually, this is where the results really differ.
> For starters, there is a highpass cutoff frequency in most (all?) of them.
> This is a problem if you want slow random modulation. Some noise generators
> only cover the audio range.
> The other problem is the random distribution. Some noise generators seems
> to be oscillators that are modulated by the noise. This has the advantage
> that the amplitude is always about the same. But the waveform isn't the
> classic gaussian distribution. If you sample it with a traditional sample
> and hold, you might not get what you want. This is the problem with the
> Matrix 6 circuit.
> 
> I suspect that for really slow random modulations, the shift register
> method is the only one that will be totally satisfactory.

If somebody is interested in long shift-register variants, if you dig
in the archives you will see a thread containing alot of usefull
info. I for instance dropped out a list of LOOOOOONG polynomials which
can provide both a dense (small apparture between frequency
components, really, really tiny actually), long loop-time (longer than the
expected lifetime of the curcuit, some of them reaching for longer
than earth, universe and everything...) and hi frequency (OK, toss em
a 50 MHz clock at least... ).

The thing is, getting these properties isn't THAT expensive. Toss a
clock at three-four CMOS chips and you are right there. Good
post-processing in a filter for pink-noise properties and you should
feel right at home.

Cheers,
Magnus