[sdiy] Digital noise generation

[Magnus Danielson]

From: mark verbos <mverbos at earthlink.net>
Subject: Re: [sdiy] Digital noise generation
Date: Tue, 08 Mar 2005 15:07:06 -0500
Message-ID: <422E05EA.2010300 at earthlink.net>

> I think the point of gaussian noise, or any specific distribution,  is 
> to tune the probability of certain voltages in control applications, 
> particularly in a Sample & Hold. When using noise as an audio source 
> simply pink, white and red are good enough. Am I wrong?

Yes. You are mixing the issues a little too much. Natural noise (thermal noise)
which is what we normally use as noise source is gaussian by nature. Then we
frequency-shape it to fit our acoustical needs. When you deal with pseudo-
random noises you have a different distribution.

When you frequency-shape noise it will be heavier on the base, which means that
it rather build large amplitude deviations of lower frequency than for higher
frequencies. Naturally, this shapes the amplitude distribution too.

My point is, most of the times, we select the noise colour for its frequency
distribution, not for their slight different amplitude distributions, which
usually is more of a control-CV aspect. It's not that there isn't differences
that follow along, but we usually select with different aspects in mind.

> In  the Buchla Source of Uncertainty modules, Don has simply +3, flat 
> and -3 for the audio noise and several specific distributions in the 
> stored voltage sections.

Indeed. A small alphabet of noise shapes... sooo handy! ;O)

Cheers,
Magnus

> Mark
> 
> 
> 
> Antti Huovilainen wrote:
> 
> > On Tue, 8 Mar 2005, Tim Ressel wrote:
> >
> >> I believe it has to du with distribution. I saw a
> >> blurb (in EDN?) about summing together 12 analog noise
> >> gens to make the distribution gaussian instead of, um
> >
> >
> > I have compared uniform and gaussian noise in matlab and heard no 
> > difference between them. AFAIK the lowpassed (cutoff at 1/16) noise 
> > approximates gaussian.
> >
> > Antti
> >
> > "No boom today. Boom tomorrow. There's always a boom tomorrow"
> >   -- Lt. Cmdr. Ivanova
> >