[sdiy] Random Voltage Generator & ADV/Cookbook

[John L Marshall]

Another issue is junction noise is *white*, energy per Hz. Even at sub-audio
we tend to *hear* or use energy per octave.

John


----- Original Message -----
From: harry <harrybissell at prodigy.net>
To: <music.maker at gte.net>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, November 11, 2001 7:09 PM
Subject: Re: [sdiy] Random Voltage Generator & ADV/Cookbook


> OKEY-dokie...
>
> There is merit to using the S/H (LFO) to sample a random noise source...
> then lag process (LPF) the result.
>
> Most junction noise sources are severely lacking in real low frequency
> amplitude... this is usually from the HPF formed by the blocking cap
> in the first stage.
>
> By sampling the wideband noise, you get large voltage variations, which
> are easier to LPF....
>
> H^) harry
>
> Scott Gravenhorst wrote:
>
> > xeno at xenoweb.com wrote:
> > >Magnus Danielson wrote:
> > >>
> > >> From: Scott Gravenhorst <music.maker at gte.net>
> > >> Subject: Re: [sdiy] Random Voltage Generator & ADV/Cookbook
> > >> Date: Sun, 11 Nov 2001 13:27:01
> > >>
> > >> > A ranodom voltage *is* noise.
> > >>
> > >> I think he wants slow changes. There is basically two types, just
slow
> > >> variations, or random steps.
> >
> > Yes, I'm sorry, I was being a smart-ass.
> >
> > >Yes! Slow changes/variations are what I'm after, not sample and hold.
> > >
> > > > The slow variation version is just a lowpassfiltered noise source,
if
> > >> you vary the lowpass filters frequency, you have more or less of the
> > >> quicker movements.
> > >
> > >So by running a 'regular' white or pink noise source through and LPF
and use
> > >that to modulate a filter, I'll get the same result?
> >
> > Yes.
> >
> > >> The random step version is a noise source with a sample-and-hold
> > >> circuit controled by an LFO. As you vary the frequency of the LFO,
you
> > >> vary the length of each step.
> > >
> > >Yep, I understand the S&H via LFO (an SH-101 was my first synth) but
I'm
> > >looking for smooooooth changes. :0)
> > >
> > >> Both these can use a common noise source, the after-processing is
> > >> simple to duplicate.
> > >
> > >So in a circuit where you can vary the speed of the random voltage,
> > >what is happening? Are you simple changing the cutoff frequency of a
LPF filter
> > >the noise is going through?
> >
> > You have it.  Depending on just how slow you want to go,
> > you may want to have an LPF that can go to very low
> > cutoff frequencies.  Subaudio.
> >
> > >> You DO get noise outputs as a side-effect.
> >
> > Which is what I was being a smart-ass about...
> >
> > >> Cheers,
> > >> Magnus - contributing to the noise - that must make me a noise
generator...
> >
> > Never.
> >
> > >:0))
> > >
> > >Thanks Magnus!
> > >--
> > >John Greczula
> > >_____________________________________________________
> > >X e N O V A T O R   T e C H N O L O G Y   A C C e S S
> > >  *Supplying Earth with Innovative Music Products*
> > >     http://www.xenoweb.com    xeno at xenoweb.com
> > >
> > >John Greczula/Xenovator
> > >Tel: 519-421-2570  Fax: 519-421-2960
> > >_____________________________________________________
> > >Sherman Productions - Sherman Filterbank
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> > >_____________________________________________________
> >
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