AW: VCO idea and env

[Martin Czech]

> You have to use full wave instead of half wave rectifiers.
> Then the segments are independent, and you *can* draw 
> the waveform (with a set of sliders, not with a mouse (;->) ).
> No problems with nonmonotonic fuctions. No discontinuousities
> (sp ??), though.,
> 
> Shameless self promotion: 
> <http://www.synthfool.com/diy/jh_ipscan.html>
> 
> For PWL applications only, you can omit half of the circuit. No VCAs,
> no VCA control path, put a slider potentiometer into each of the
> LED driver paths, and sum all the slider output voltages together.
> 

Sorry Juergen, I have a hardcope of that circuit at home, totally forgotten.

Wow!

And now, as you say this, I see how a multi segment analogue envelope
generator could be done. We take a Haiblesian (sp?) interpolator, each
segment at a fixed position, so that neighbour channels meet at 50%,
and when one arrives at 100% the two neigbours must be at 0%.  The
input voltage for each segment is the breakpoint level, whereas the
scanning rate makes the breakpoint slope steepness (simply: the time).
And voila: time and level are perfectly decoupled! Something I gave up
to think about, cause I thaught this decoupling would be only possible
in the digital domain. The scanning waveform is a weird sawtooth, with
segments of different slope, but always rising. And even a constant
output feature is possible, no problems with too small charging
currents, the scanning waveform moves on, but the channel inputs are
the same, thus no output change.

I know, there was a thread about linear vs. exponential vs. log
envelopes.  I have the feeling, that this could be realised by the way
the scanning "sawtooth" is integrated, linear or exponential or log
(with saturation).  This feature could be switchable for every segment
individually.

One little comment I can't suppres: The above mentioned .html document
always says that triangle waves are used for scanning (am I right?).
But this means that every interpolator stage appears TWICE in one
cycle.  This is not quite what one expects, if you are going do "draw"
a PWL.  Instead a sawtooth wave should be used (what happens on the
"flyback" ?  glitches ?) I ask this not to annoy Juegen, but maybe I've
not understand the circuit.

m.c.

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