AW: Serge Waveshaper was Re: Harmonics question

Haible Juergen Juergen.Haible at nbgm.siemens.de
Fri Jul 3 17:12:20 CEST 1998


>  SC> The second section is...well, no one really seems to know (prove me
> wrong,
>  SC> folks!). It seems to work as follows: When the signal voltage reaches
>  SC> certain thresholds (positive or negative), the signal "wraps around."
> Easy
>  SC> to do in digital (the Nord Modular implements it, and it sounds
> GREAT), but
>  SC> I don't know how to do it in analog. 
> 
I was going thru this thread once more (sorry for the late reply), and then
I
made some experiments with my Interpolating Scanner (schemos and
full description finally on my page at Synthfool), set to waveshaping mode:

When I set every even breakpoint to maximum, and every odd breakpoint to
zero,
I can create a "zigzag" courve, i.e. a triangle waveform in the voltage
domain.
When I modulate this with a normal (time domain) triangle wave of increasing
amplitude, I get a result that *might* be close to the one you described:

The output starts with a triangle wave at fundamental frequency, and at some
point
the peaks are folded back to become ever increasing tringle shaped dents.
At some point, there is a triangle with higher frequency,
and soon after that the peaks of this wave are folded back, too. And so on
to
higher frequencies.
I do not know if this is what this famous Serge module does (can anybody
check this on a real Serge waveshaper?), but if that is the case, it's very
easy to clone, because we'd only need a fraction of the Interpolating
Scanner's
circuitry for that: Omit the VCAs, and omit every other channel completely
(triangle functions not overlapping anymore, but touching the neighbouring
one at its base). Speculating further, I bet Serge has build his module
around
3900's and not saturated pnps. Let me see, one 3900 for 4 triangles, so you
can imagine to what high number of maximum harmonics one can get with a
handful of these chips.

What do you think ?

JH.



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