[sdiy] Dealing with velocity sensitivity / scaling on envelopes

[Richie Burnett]

> ...So what should I do? Attacking downwards seems completely wrong...

Maybe try heading towards the new velocity-scaled attack destination with 
the "attack" time-constant if it is above the current envelope level, or 
head towards the new-velocity scaled destination with the "decay" 
time-constant if it is below the current envelope level.  That might feel 
(and sound) more natural?  It also gives you the ability to keep the 
envelope smooth (continuous without steps) by choosing suitable attack and 
decay times, or you can get a quick step response if you want to by reducing 
the attack, decay, or both controls down towards zero.

It's might also be worth mentioning here that analogue envelope generators 
often respond to the user changing the sustain level during a held note by 
heading towards the newly set level using the decay time-constant.  This is 
regardless of whether the new sustain level is above or below the current 
envelope level.

Unfortunately I don't have a velocity sensitive analogue monosynth, 
otherwise I would test it and get back to you with some real-life results.

-Richie,