VC ADSR

[macdonald at evenfall.com]

Hi Guys,

> >I like your transistor input circuit. Was Chris' schematic wrong about the
> >trigger in on the 555? I thought it needed to go negative...
> 
> Wellllll....yes. You are correct, Chris' circuit trigged on key up not key down.
> That is a little unnatural feeling. I'm sure he would have gotten that fixed.

Not sure what is meant by the above.  Here's how the 555 works in my
circuit:

Trig   Thresh   Out
----   ------   ---
 0        x      1
 1        0      1
 1        1      0

So when the trigger is held low (i.e. gate is low) the threshold input
is masked and the output remains high regardless of threshold input. 
When the trigger input goes high (gate high), this unmasks the threshold
input, allowing it to detect the attack peak.  Once the threshold level
has been reached the output goes low.  Since the 555 output is connected
to a selector input on the 4052, this has the effect of switching the
4052 input when the envelope attack peak is detected.

-Chris