Dialog still rolling

[Kimmo Koli]

Well,
I have to disagree, VCOs DO have a sound of their own, even with the basic
waveforms. Some VCOs may sound fat some firm and DCOs thin. 

Q: Why ?
A: Noise, more accurately phase noise !

Noise in oscillators affect the oscillating frequency, so noise in a
VCO is like small amount of FM with white or shaped noise. And VCOs
are the noisiest frequency sources ever built, some may perform better
and some worse. Also some amount of cross- and selfmodulation due to
limited PSRR gives even more characteristics to a VCO sound. 

And phase noise has nothing to do (okay, some but not much) with long term
drift. A VCO may be very temperature stable but can still have lot of
phase noise. And even the quality of the PCB may affect the sound.

So more nonidealities in VCOs = fatter sound. But how fat you like it,
is another issue altogether...

Best regards, Kimmo Koli <kimmo at ecdl.hut.fi> 

On Fri, 18 Apr 1997, Paul Schreiber wrote:

> Hey, this is the most fun on here in weeks!!
> 
> > First, no VCO has a "sound", sterile or otherwise. They may have THD,
> >but a pulse is a square is a saw. But what they DO have is drift and have
> >linearity errors. 
> 
> Q)But THD and drift are such an important part of a VCO's "sound" - how can 
> you just disregard them to justify a VCO's lack of "sound"?  Sometimes 
> you want a clean, clinical VCO like a 3340, sometimes you want something 
> whacky like a 303 VCO.  It's easier to build a VCO you like the 
> sound of than to take a 3340 and selectively mess it up to sound the way 
> you want in different circumstances.
> 
> A) I'll restate this. One VCO sitting there doesn't have ANY sound quality. 
>  Neither does my HP function generator. What does have "sound quality"
> is multiple VCOs happily drifting against each other. Now what's
> interesting is the following: when do we want 'wacky' (JD's word) versus
> 'clean'?? I suppose it depends entirely on what sound(s) you are trying
> to make. If you're Wendy Carlos, trying to lay down 8 parts in 16
> hocketed timbres, the whole mess microtuned to 18 notes/octave, then by
> God, you want stability. However, if you are trying to do the Pink Floyd
> "Meddle" VCS-3 stuff, the driftier the better. What is interesting about
> a DCO is you can algorithmically "screw up" the tracking in infinite
> ways: apply Gaussian noise, triangular PDFs, Rayleigh channel fades
> (sorry, I'm getting carried away). In other words, with a little
> experimentation emulate ANY VCO response you want: from "3340" to "PAiA"
> <grin>. And the digital circuitry is easily expanded to 32 to 64
> independent outputs simultaneously.
> 

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   Kimmo Koli                         Helsinki University of Technology 
   kimmo at ecdl.hut.fi                  Electronic Circuit Design Laboratory
   http://www.ecdl.hut.fi/~kimmo      P.O.B. 3000
   Tel:  +358 9 451 2273              FIN-02015 HUT
   Fax:  +358 9 451 2269              Finland 
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