Tom Henry Tunable Noise Source

jhaible jhaible at debitel.net
Thu Nov 18 00:51:11 CET 1999


Thanks !
Though I don't think it answers all of my questions, it's a very
useful picture.

JH.

----- Original Message -----
From: Grant Richter <grichter at execpc.com>
To: Haible Juergen <Juergen.Haible at nbgm.siemens.de>; jhaible
<jhaible at debitel.net>; Martin Czech <martin.czech at intermetall.de>;
<synth-diy at mailhost.bpa.nl>
Sent: Wednesday, November 17, 1999 11:16 PM
Subject: Re: Tom Henry Tunable Noise Source


> Hi Juergen, Don, Martin,
>
> I have a poster which was put out by the
> Federal Scientific Corporation that shows all this probability
> distribution stuff. Titled heavily enough
> "Typical functions in the time and frequency domain
> with amplitude probability density and cumulative distribution"
> Whew!
>
> I have scanned it in and put it up at
>
> http://www.execpc.com/~grichter/probability.htm
>
> the graphic is large ~111K so wait for it to load.
> I think it addresses all Juergens original questions
> and is also just a good reference
> (I hang it over the workbench)
>
> Grant
>
> ----------
> > From: Haible Juergen <Juergen.Haible at nbgm.siemens.de>
> > To: Grant Richter <grichter at execpc.com>; jhaible <jhaible at debitel.net>;
> Martin Czech <martin.czech at intermetall.de>; synth-diy at mailhost.bpa.nl
> > Subject: RE: Tom Henry Tunable Noise Source
> > Date: Wednesday, November 17, 1999 4:35 AM
> >
> > >> (3) How is the pattern (distribution ?) of a Sample and Hold
> > changed when
> > >>       you're sampling a white-noise-FMed VCO instead of sampling
> > the
> > >noise
> > >>       directly ?
> > >
> > >I can answer this one for certain.
> > >
> > >White noise has a gaussian (bell shaped)
> > >probability distribution relative to amplitude.
> > >The further from zero volts the lower the
> > >probability of getting a sample.
> > >
> > >A triangle of sawtooth wave sampled from
> > >a VCO modulated by white noise has and
> > >equal probability distribution. All voltage levels
> > >have equal probability of being sampled.
> >
> > Hi Grant, thanks for your answer!
> >
> > This is what I was *hoping* for: a means
> > to get equally distributed random samples.
> > Now if I'm sampling a fixed frequency triangle oscillator
> > at a fixed sampling rate, I get equal distribution of
> > discrete levels, but they form a regular pattern in time,
> > depending on the VCO freq and sampling rate.
> > This is obvious for LFOs (the famous OB-8
> > sampled LFO waveform), but it even happens with
> > very high VCO frequencies. (I guess the sampling
> > folds any high VCO freq. partly into the baseband.)
> > Now with white noise modulating the VCO freq one
> > can destroy the regular pattern quite easily.
> > But there's still questions remaining (for option (3)):
> > What amount of FM with noise will be enough to get
> > no audible repetition in the S&H pattern ? And will
> > the equal level distribution of a sampled triangle VCO
> > be in any way disturbed by the noise-FM ?
> > What I *fear* is that if you get away from regular patterns
> > you might also loose the equal distribution. But it's
> > a very nonlinear operation, so I don't know the answer.
> >
> > JH.
>
>





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