[sdiy] Wondering about function generators for envelopes

[Seb Francis]

Personally if I were to make a multi-segment envelope generator I think 
I would do it with a PIC or something ... it really shouldn't take more 
than a few components ...

n 'level' pots
n 'time' pots
uProc with built in A-D for reading pots
n-way mux to scan pots
DAC
opamp output buffer

With a 20MHz PIC it ought to be possible to get very fast+smooth 
envelopes out.  I managed to squeeze 2 envelopes + 2 LFOs out of my 15 
channel MIDI->CV converter running on a 20MHz PIC without any noticeable 
stepping even with very fast envelopes.  In comparison to this, the 
software for a basic multi-segment envelope generator would be very simple.

Seb



Tim Parkhurst wrote:

>>-----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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