Digital EG/LFO (was VCOs & Tempco)

[KA4HJH]

Colin wrote:
>The voltage controlled envelope generators in my modular use an analogue
>switch (4053 or 4052 - can't remember! the dual 4 into 1 type), a
>flip-flop and a comparator to switch the various rate and level voltages
>to a LM13700 slew generator with has an expo convertor on the control
>input to give a useful control law. It would be simple to adapt this
>circuit for processor control in the way you describe.
>The only doubts I have are where a large number of envelope generators
>are required  - what effect on the sound might there be if the processor
>is under heavy load.
>One solution to this might be to use a separate processor on each voice.
>Then it would only be driving 3 or 4 envelopes at most. Another control
>line could be added to switch the slew generator between linear and
>exponential curves.

Do you have a schematic of this? I'd love to see it.

Actually, a 1 Mhz microcontroller shouldn't have any trouble running a
dozen of these things. All the work is being done in the real world. The
troublesome part is the front end. One possibility would be to have a
separate unit with an LCD display that programs all of them. And you're not
just limited to ADSR. You could have any arbitrary number of breakpoints.
That's the beauty of software (assuming your processor can do it in real
time). And you could be spitting out sync'ed LFO's at the same time (with
morphing fractal waveforms in octature, if you like). Of course the thing
has both MIDI and gate/trigger inputs. After I get my SEM's patched out I
might just build one of these...


Terry Bowman, KA4HJH
"The Mac Doctor"