[sdiy] State Var Filter with Nonlinear Feedback

[Scott Gravenhorst]

"Ian Fritz" <ijfritz at earthlink.net> wrote:
>Scott --
>
>Looks like a very interesting experiment.
>
>> 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.
>
>Is this because your non-linear elements clip at a fairly low voltage? (Just
>guessing.) Maybe rescaling the levels so you get more gradual changes would
>be something to look at.

Actually, I hadn't tried clipping, and I should. So far I have
only tested inline stuff like inverse parallel diodes.

>
>> 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.
>
>Well, what if you track the VCO and the VCF together? Then wouldn't you
>always have the same effect?

This is a 'must try'.  (FatMan is down right now, so that's
next on my list, fix that and try this).

>> It will also go chaotic at points as well as into
>> self oscillation.
>
>That could be interesting -- can you get chaotic effects at low frequency?

Most of my experimentation was well into the audible range.
I also need to test this.

>> I tried several different nonlinearities, but they
>> all seemed to have similar sonic characteristics.
>
>Sometimes it pays to look closely for more subtle effects. For example, some
>people will say that all multistep waveforms sound the same .. but if you
>have a sound in mind that you are trying to zero in on, suddenly they don't!

Yes, you're right.  I need to spend alot more time with this
hooked up to a synth instead of a sig-gen.

>> 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.
>
>Too bad it hasn't worked out the way you expected. But sometimes if you look
>at things the other way around -- what can I do with what I've got -- you
>come up with useful results.

These are good suggestions.  Which is probably why I posted my
message of dispair.  I knew this list would provide help.

>
>  Ian
>

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