[sdiy] VCO Jitter, Slop ... (was: Re: Smith's Evolver Desktop's spikey VCO waveforms)

Andre Majorel aym-htnys at teaser.fr
Mon Jun 10 18:57:05 CEST 2013

On 2013-06-09 03:00 +0200, Michael Zacherl wrote:
> On 9.6.2013, at 00:11 , Andre Majorel wrote:
> >> VCOs suck.  That's why they're interesting.
> > 
> > I can't prove it but I'm pretty sure it's their jitter that
> > makes VCOs interesting, more than their waveforms. For human
> > ears, all waveforms are equally boring if perfectly periodic.
> if you had to put it into numbers, what would be the amount of
> jitter, you think?

Hi Michael. Don't know. I experimented with modulating the
frequency of an MS-20 VCO with white and pink noise. As the FM
sensitivity knob was turned clockwise, it went from no audible
effect to unpleasantly warbly. I couldn't find a setting that
made it sound "even fatter" or anything like that.

My guess is that there is a rather narrow range of jitter
between "sterile and brittle" and "blurry and weak" and by a
happy accident, the state of electronics in the sixties and
seventies led to VCOs which fell right in the middle.

Recently read a very interesting bit about how much mains
frequency ripple there is on power rails inside synths. Wish I
could remember where and who.

Some years ago, Scott Gravenhorst posted here an MP3 of one of
his digital synth projects. I thought it sounded surprisingly
good (i.e. not DCO-like). He said he used a small amount of pink
noise FM on the oscillators. Maybe he could tell us more.

> et al ... and, in general, something like a slop parameter on
> DSI synths for their oscillators, is that just for the
> frequency and how much? Never had a play with it.

Since you can hear the difference between VCO and DCO on a
single note, I don't see how temperature drift & scaling errors
could be the source of "fatness". They may contribute to it, but
they're not the essential ingredient.

André Majorel http://www.teaser.fr/~amajorel/

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