[sdiy] Yet another 292c Lowpass Gate audio sample uplaoded

[Grant Richter]

> 
> 1)  No pop.  Do the same thing using a standard VCA,  with an envelope as
> short as the one I have used and the usual VCA crack*pop*snap will be heard
> as it opens and reacts to the voltage applied.  The vactrol in the lowpass
> gate by comparison affords a slight smoothing of control voltages as the led
> turns on.

Optically isolating the control signal has advantages. In the Buchla 200
Music Box, the only transconductor used is lots and lots of Vactrols. So the
audio path, and the control path have completely separate connector types,
power subsystems and ground systems. The Buchlas use an 8 wire power
harness. Ouch!
> 
> 2) The ringing in 'combo' mode.  When the Low pass gate is set so that the
> switch is on the middle position, one hears a mix of the standard VCA and
> the low pass gate in equal amouts.  The net effect of this is a wonderfully
> natural sounding ringing  which is very audiblet with short envelopes like
> I've used here  Chalk this up to the vactrol LED now dimming off and the
> removal of the .0047 cap within the circuit.
> 

The slew rate of the Vactrol slows down as the resistance increases. By luck
or design, this mimics the effect of acoustic systems ringing longer at
lower frequencies.