[sdiy] Wondering about function generators for envelopes

[Tim Parkhurst]

> -----Original Message-----
> From: Metrophage [mailto:c0r3dump23 at yahoo.com]
> Sent: Thursday, July 07, 2005 12:38 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Wondering about function generators for envelopes
> 
> I don't know much about analog computation, I wonder why people don't
> make more varied kinds of envelope generators. Is it because more
> complex functions are difficult to make, or because people aren't
> interested in more varied envelopes? Not neccessarily "arbitrary", but
> just different than setting four amplitude levels. Say, for instance,
> four (or more) points with controls for how quickly we go between them,
> amplitude of each point, and ways of describing various transitions or
> interpolations between them. Or even just modules for a function which
> offers a few variables which produce decent musical envelopes. It
> seems
> obvious, but I never see anything like this. All of my web searches
> yield endless links to benchtop function generator units, rather than
> people designing and making various kinds of functions. I have Korn
> and
> Korn's 1950's book on computation at my parents house, but it being
> all
> tube-oriented is a bit confusing to me.
> 
> Does anybody do this sort of thing? Using a sequencer, Jim's cool EG,
> rate-settable and/or chainable ADSRs sounds neat - but there is
> something else which should exist that eludes me.
> 
> CJ
> 
******************************************************
Hey Metro / CJ,

A couple of thoughts about envelope generators...

If you look at it, the standard ADSR is easy to build, easy to program, easy
for even novices to figure out, and does a pretty good job of making
musically useful envelopes. You've got a handful of components, four knobs,
and you're good to go! If you want to get exotic, add a trigger delay or
voltage controlled times or even a self-triggering/LFO mode. 

Want to get even more exotic? Build two or three AR/AD or ADSR types and mix
the outputs together. All sorts of weirdness with double blips and neat
stuff like that.

To really go much beyond the standard ADSR type EG, you need to build a
"time / level" sort of arrangement. All of the sudden you've got a lot more
knobs and parameters to deal with (even a four step version has a minimum of
eight knobs), and on some designs, changing one parameter affects another.
On many time/level designs, changing the level affects the time. A lot more
circuitry is required to eleiminate this interaction. 

So basically, the standard ADSR (or two or three) is simple and works well.
Agreed, there are places where an exotic multi-step envelope is really cool,
and I don't want to discourage you from trying something new, but there is a
lot of mileage still to be had from the 'old faithful' ADSR. 



Tim (my knobs interact, too) Servo

"Imagination is more important than knowledge." - Albert Einstein





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