[sdiy] Combined CV/Gate on a cable

[Tim Parkhurst]

> I've never quite understood the point of having separate gate & trigger
> signal. To me it seems that they could trivially be combined to one gate
> signal that simply goes to zero for a very short time every time there's a
> new note (if the old note is still on).
> 
Generally, the trigger signal is used to "restart" the ADSR and make it go
through the A and D cycle even if other keys are already being held down. If
the ADSR is designed right, what you get is just the portion of the A and D
that would be heard above the sustain level (so the envelope doesn't start
over, the sustain voltage stays on). The gate signal simply stays high as
long as a key is held down (so it lets the envelopes know how long to
sustain). 

Maybe I can explain this better... Look at the (rather crude) drawing below.
The cycle starts when a key is pressed and both a gate and trigger are
generated. Now if the key is held down, the envelope sustains. But if you
press another key while still holding the first down, only a trigger is
generated (the gate stays high) and only the portion of the envelope above
the sustain level is retriggered. Basically, this is to allow playing legato
on a monophonic keyboard. Hopefully this explanation makes sense and the
diagram doesn't get wrapped around and messed up :)


Tim Servo
"Give a man a fish and he will eat for that day.
 Teach him how to fish and he'll spend all his money on fishing gear."




    *                           *
   * *                         * *
  *   *************************   *************************
 *                                                         *
*                                                           *

Gate (key held down)           first key still held        all keys released
Trig                           Trig only                    



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