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

Tom Wiltshire tom at electricdruid.net
Mon Jun 10 22:10:09 CEST 2013

JH argued that linear drift/offset was a significant part of "fatness" in oscillators. A detune of a few 1/10ths of hertz gives motion, without sounding out of tune. Doing this with a V/Oct CV leads to errors becoming increasing large as you go up the octaves, rapidly becoming unpleasant.


So however much drift you apply, perhaps it should be linear FM, rather than into an exponential FM input.


On 10 Jun 2013, at 17:57, Andre Majorel <aym-htnys at teaser.fr> wrote:

> 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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