[sdiy] VC Chaos

[Ian Fritz]

At 01:01 PM 11/30/2004, ASSI wrote:

>I've just had a listen and I must say I'm blown away... especially
>Wattor is quite nice. Would you mind detailing the setup for the demos
>and how stable or repeatable the settings for the chaos generator are?

Glad you liked the demos.  I just played around with the system driving 
some simple modular patches for a few hours and recorded several 
interesting results.  The first demo is a VCO with AM growl driving a 
VCF.  The main variable (x) is controlling the VCO pitch, x' is controlling 
the filter freq and x'' is controlling the AM depth.  The idea was to 
demonstrate how the three signals can work together to produce a somewhat 
"organic" effect (more motion gives more filter sweep and more filter sweep 
gives more growl) and to illustrate the idea of a sound that is "always 
changing but always the same".

The "Wattor" patch includes pulses produced by a trigger-generating circuit 
with a threshold, so only large-amplitude phase space paths produce 
triggers.  This subset of zero crossings gives the  accented notes.

The chaos generator is somewhat tricky to set up, because of the high 
sensitivity to the parameters and because changing frequency also causes 
the pattern to change a bit.  This latter effect is a result of OTA CV 
feedthrough, which changes the loop offset voltage.  T stability can be 
improved by biasing the OTA input diodes on, and of course by using a 
compensated expo converter for the freq control.  These things I am working 
on now.

   Ian