[sdiy] State Var Filter with Nonlinear Feedback

[Scott Gravenhorst]

I finally got back to this to see if it's worth
anything to me and in a word, for me, it is not.

It can add harmonic content, but not across a 
wide bandwidth, rather the distortion kicks in at points
where the input signal's harmonics correspond to
that of the filter's Fc setting.  When sweeping
Fc the harmonics seem to pop in, like there are detents.
At least that's what it sounds like.

Maybe I need to play with more complex waveforms??  I
used square, pulse, saw, tri and sine.  All get very
well screwed up, but not in a way I would call musically
consistent or useful.  Ie, you might get a cool effect 
on one note, but play a semi up or down and it's gone.

It will also go chaotic at points as well as into 
self oscillation.

I tried several different nonlinearities, but they
all seemed to have similar sonic characteristics.

At the very least, I can convert it into a plain old
VC-SVF, so all is not lost.  Scoping around in it,
it appears to be doing what it should, however 
I'm just rather underwhelmed by it's sound altering
usefulness.

Schematic is at 

http://home1.gte.net/res0658s/Electronics/nonlinear_filter.gif

for anyone interested.

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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