Idea for an envelope generator

[gstopp at fibermux.com]

     Okay I think I get it - the A row sets both the comparator reference 
     "window" and the "goal" for the slew limiter to slew to, and as soon 
     as that voltage on the selected pot is reached, move on to the next 
     step. The B row sets the slew time for each step.
     
     To start and stop, it seems to me that you need a "n + 1th" step, 
     where n is the number of steps in the sequencer. The Moog 960 has that 
     - a ninth step where no pots are selected. So hit the thing with a 
     step trigger to start it, let it trigger itself along, and let the 
     trigger from the last step "fall off the end".
     
     Potential problems: first, the B row is not really time, just slope. 
     The bigger the voltage difference between consecutive steps, the 
     longer the slew will take, for a given slope. Second, if three row A 
     pots in a row were set to the same value, would the comparator ever 
     trip to advance to the next step? If there ever were a trigger "lost", 
     then the thing would hang up and need another external trigger to 
     finish. But then again that may lead to interesting sounds....
     
     Good thought experiment however!
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Idea for an envelope generator
Author:  Christopher List <Christopher_List at sonymusic.com> at ccrelayout
Date:    1/30/96 2:52 PM


I was thinking about something for an n-step envelope generator today and I 
wonder if anyone's tried it (I've got so many circuits in the works now that 
it'll be a while before I get to play with this one).
     
Suppose you had a two channel sequencer (analog, of course). 
Make channel A your voltage levels and channel B is your delay times. 
You run the output of channel B into the CV of a linear VC slew limiter. 
You split channel A. One line goes into the input of the slew limiter. The 
other line goes into two amp amp circuits. One adds a millivolt, the other 
subtracts a millivolt - these two signals become the high and low reference for 
a "window comparator" (two comparators and a NOR gate, I think). The output of 
the slew limiter is your envelope output and also get's routed into the input 
of the window compator. Lastly, the output of the comparator gets routed back 
to the trigger input of the sequencer.
     
Is there an easier way of comparing two voltages?
     
I haven't worked out the logistics of starting / ending the process - any 
suggestions?
     
Has anybody tried this? - I haven't built a sequencer yet, but it seems like it 
would be a cool mod for an existing sequencer. You could just put in an "auto 
step" switch which would route the signal through this circuit and automaticly 
step the sequencer as it reached each value...
     
-CL