[sdiy] Wondering about function generators for envelopes

[Aaron Bader]

On Thu, 7 Jul 2005 12:38:16 -0700 (PDT)
Metrophage <c0r3dump23 at yahoo.com> wrote:

> 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.

I actually made a sketch of something that did just that a few weeks
ago, but haven't really had time to play with the idea further:

http://www.louisville.edu/~adbade01/arb-wave.png

Use a presettable down counter and you could choose how many points you
want to use, but, that would also require wiring the points backwards.
The only flaw in this design right now is amplitude modulation would
effect frequency; It was included because it's a trivial to implement
and possibly useful enhancement.

My plan was to use a 4046 to phase-lock-loop it to an oscillator, thus
making an arbitrary waveform in the audio range. Choose a higher value
capacitor and it would work quite well as an lfo, or some way to make it
stop after hitting a preset number of points and continue after the gate
lets off and you'd have a good envelope generator a-la CZ-1000 or DX-7.

I never thought about different transition types, but, I guess you could
take output from the amplitude control for a squarish shape, from the
capacitor for a triangular shape... getting a good exponential
decay/gain would be interesting but I'm not sure where to start with
that.

-- 

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