SV: Re: [sdiy] Noise as one unsteady tone!

[Magnus Danielson]

From: karl dalen <dalenkarl at yahoo.se>
Subject: SV: Re: [sdiy] Noise as one unsteady tone!
Date: Tue, 6 Sep 2005 04:30:17 +0200 (CEST)
Message-ID: <20050906023017.31461.qmail at web25504.mail.ukl.yahoo.com>

> 
> --- Richard Wentk <richard at skydancer.com> skrev:
> 
> > At 12:07 05/09/2005, Magnus Danielson wrote:
> > 
> > >If you have a very selective filter you will find an unstable "tone"
> > anywhere
> > >you look, but what you hear is nothing but a narrow filter stimulated by
> > noise
> > >and not a characteristic of the noise itself. Not that it is not usefull,
> > but
> > >it is a different matter.
> > 
> > This is one of those times where theory collides with the real world.
> > 
> > In reality if you patch together enough sine oscillators - like a few 
> > thousand - spread randomly across the frequency band, you get a reasonable 
> > approximation of noise.
> 
> The reason i asked  was that i recently did some laborating with
> PM, two VCOs and a delay line, this gives pass zero modulation, 
> but strangely enough it sounds better then two pass zero oscillator,
> one modulating each other, more dynamic, the wave looks different too.
> 
> In the PM example modulate enough and noise are created wich would be 
> the same as your suggestion, ie at strong modulations the wave folds
> over so many times and by doing so the amount of dissplaced overtones
> in the end creates noise. Supricingly it seams, at least on the scope,
> the power spectrum of the noise seams quite uniform!
> 
> So, then i comes to this, i have two VCOs and a delay line both
> a reproducing a steady tone, one are used as carrier wave the other
> modulates the time delay, enough modulation and i have noise, 
> the fundamental and all the overtones move up and down in 
> frequency to the frequency of the modulator wich tells us
> that noise can be of different origin, tousands of steady 
> sine waves or a simple mowing frequency PM setup!....No? 

Well, almost. When you do excessivly deep PM with a delay-line, you "open up"
enought Bessel terms of side-tones that they create a fairly dense spectrum.
Here you will notice the difference between PM and FM, so if you where doing
the same thing with linear FM it would behave quite different. If you insert
an integrator between the modulating oscillator and the delay line CV input
you have the FM case.

A dense set of sines do in some degree behave as noise but also as a tone with
chorus. It all depends.

Cheers,
Magnus