Sitars and Waveshaping

Sean Costello costello at costello.seanet.com
Fri Jan 16 07:51:19 CET 1998


Hi all:

Anyone have any idea what type of waveshaper could be built to simulate a
sitar? I can't even think of where to begin looking for clues.  The sitar
seems pretty nonlinear (the buzzing sound is caused by a curved bridge);
conventional synthesis doesn't seem like it would simulate it too well.  It
would be great to build a box that would create sitar-like effects that
would be volume-dependent, so as to work with guitar (or with synth, if the
waveshaper is preceeded by a VCA).

Also, anyone out there have much experience with cool waveshapers?  I would
love to build circuits much like the Serge Wave Multiplier.  As far as I can
tell, the Wave Multiplier works as follows (these are just guesses - I have
never looked inside of one of these beasts):

- The first section is simply a VCA followed by a clipping amplifier.  The
clipping amplifier rounds the wave.  Is this just diodes, or is it something
more complicated, like an overdriven differential amplifier?
- The second section is probably a "diode breakpoint" generator.  I still
don't know what this is, but Paul Perry said that this would produce the
described behavior (where a given signal will reverse direction, or "fold
over," at certain voltage points, producing a sweep of odd harmonics with a
triangle wave).
- The bottom section is an LM3900, rigged up as a voltage controlled
full-wave rectifier.  Serge Tcherepinin (sp?) has a patent, in which he
explains how each stage of an LM3900 can be incorporated (with a few
resistors and diodes) into a voltage controlled full-wave rectifier - the
control voltage can be used to change the amount of rectification, from none
to full.  These stages can be cascaded for dramatic timbral effects - 3 such
stages are probably used in the Wave Multiplier.

Does anyone out there have any other cool waveshaper circuits? Anyone know
more about diode breakpoint generators?  That would also be a cool circuit
for guitar. A nice resonant filter through these circuits would probably
wreak beautiful havoc.

Thanks,

Sean Costello






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