[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.

http://www.jhaible.com/living_vcos/jh_living_vcos.html

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

T.


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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