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

[karl dalen]

--- Magnus Danielson <cfmd at bredband.net> skrev:

> > --- 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.

But,,,,,,,there has been discussions in the past on the 
difference between PM and FM and as i can remember lin FM 
are PM, vice versa!

I can se that to, but what would be the rason that you get more bessel
terms in a delay line then pushing the phase in a pass zero osc, i dont 
get that at the moment? (no maths please) :-)

In wich book did you read this?

> 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.

Hmmm, it seams to me that even in the old days it could have been a cheap
way to get PM/Lin FM by using two sine/triangle models and a very short 
delay cell.

But why would the integrator funktion cause FM if the integarator
are absolutely linear wouldent that result in to the same, ie
it integrates whatever shape are passign to its input.

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

It would be interesting to test the tousand sine example to se what it ends!

KD