[sdiy] Fast envelope generation

[Russell McClellan]

I remember being quite impressed with envelope section in the Access
Virus digital synth manual - nominally, it only has linear envelopes,
but you can use the modulation matrix to produce exponential or log
curves by routing the envelope level back to the attack, decay, or
release parameters.  I think that's a clever and intuitive UI for
users and it must have been relatively easy to implement.

Did this idea come from some analog device?  I'd be quite surprised if
it didn't and it very much has the feel of buchla or serge or some
banana system.

Thanks,
-Russell