Weird Osc sync (Was Re: triggered s&h, in phasers or modules?)

[Jones, Rodney]

-----Original Message-----
From: Robert H. Rickner-III [mailto:rrickner at zoo.uvm.edu]
Sent: 27 January 2000 16:40
To: synth-diy at mailhost.bpa.nl
Subject: Re: Re: triggered s&h, in phasers or modules?




On Wed, 26 Jan 2000 WeAreAs1 at aol.com wrote:

> 
> In a message dated 1/26/00 7:17:44 PM, you wrote:
> 
> <<Will this work with any LFO, ie could I add a trigger input to one LFO
and
> run in a S&H for wacky LFO possibilities? >>
>> 
>> It will work with most LFO circuits, especially the typical one found in
most 
>> synths (two opamp stages:  triangle integrator followed by comparator
with 
>> squarewave output).  What synth would you like to modify to have a
syncable 
>> LFO?
>
> Well, I'm trying to build a modular synth and am collecting scematics from
> the web to choose the initial modules, mostly from the efm related
> pages.  So, I'd like a whole bunch of functions more than just another
> analogue synth, I have a Matrix 6 for that, so I'm interested in any
> modifications and modules that aren't available normally.  I don't want
> the syncable lfo as much as I want the weird effects when you choose a
> trigger time different from the lfo.
> Rob cut/generic


I bought a burned-out EMS Synthi A, a long time ago, and rebuilt it into a 6
Osc duophonic beast, and with the help of a friend who was an EMS techie,
added a whole bunch of unusual features. To me the most intriging was a form
of oscillator sync I haven't come across since. 

If I remember correctly, if you were listening to VCO2 which was synced to
VCO 1 (level=0), as you attempted to vary the freq of VCO2, the actual
frequency wouldn't change, but you'd hear the familiar soft sync sound. As
you continued to move VCO2 further away from VCO1, the frequency would jump
to next pythagorean harmonic. So if you frequency modulated VCO2 with (say)
a 0.2Hz triangle, you'd hear a musically pleasing appeggio with an unusual
character since the soft sync would start again after each 'jump'.

I've heard it a few times in popular music, but the only one I can bring to
mind is on Joan Baez's 'Diamonds and Rust'.

This was a simple mod to the EMS VCO. I'm not sure how it would be achieved
on modern VCO designs, but if it's possible it could probably be done for
minimal cost.

To Rob, I'd say if you you can find out how to do this, you should seriously
consider adding this feature. If anyone knows how to do it, please let me
know!

Rod
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