Mon Dec 20 13:15:38 EST 2010

Next step

Playing a bit with basic electronics, the next step is to make that
digitally controlled device.

Rationale: the "analog" sound comes mostly from non-linearities in the
signal chain, so you want signals that see any kind of nonlinear
feedback to be analog.  Control signals can probably be digital and
"clean" linear filters, i.e. those that never see any clipping or
other distortion, could probably be digitized also.

About VCF: the simplest approach is to use BJT g_m biasing or diode
small signal resistance to set filter poles.  This requires
temperature compensation, which could probably be done digitally too.