[sdiy] State Var Filter with Nonlinear Feedback

[harry]

Craig Critchley wrote:

> Does your scope do an X-Y display?  I believe if you hook one axis up to the
> LP output and the other up to the BP output, you should get some sort of
> "butterfly" pattern when the filter starts becoming chaotic.

If you run the audio input input to X and the filter out to Y you will get
a  graph of "Lorenz Attractors".  I used this to make a "Laserium" display for
my college roomates (with a HOT scope trace and a big lens in a VERY dark
room...   Just an ordinary filter with resonance will be 'chaotic'

H^) harry

>
>
> I've been wanting to try some chaotic stuff myself; maybe I'll try building
> your circuit...
>
>                     ....Craig
>
> ----- Original Message -----
> From: "Scott Gravenhorst" <music.maker at gte.net>
> To: <synth-diy at dropmix.xs4all.nl>
> Sent: Thursday, October 18, 2001 6:03 PM
> Subject: Re: [sdiy] State Var Filter with Nonlinear Feedback
>
> > Ahhum...,  weakened attractors.  This makes very much sense.
> > I've noticed that getting chaotic behavior can be tricky.
> > One thing I see in my schematic is a 20K resistor that passes
> > a dry version of the feedback signal.  I think there should be
> > a 500K to 1meg pot in series with that so that I can better
> > control the mix of dry and distorted signal.  This would allow,
> > I think, more control over how weak or strong the attractor is.
> > Right now, I can change only the level of the distorted version
> > of the feedback signal.
> >
> > grichter at asapnet.net wrote:
> > >This is why it is called an "attractor" the function is attracted to
> stable
> > >points which are numeric multiples. Unstable intervals between the
> attractor
> > >points are the actual chaotic behavior. A good example is a flute, the
> > >"chiff" is chaotic behavior and the tone is when the energy settles into
> a
> > >stable attractor.
> > >
> > >It can actually be difficult to get at the chaotic behavior. Depending on
> > >the coefficients, the attractors may be so strong, the circuit will not
> > >operate in the chaotic mode. A solid tuned pipe has very strong
> attractors
> > >(tight seal on flute pads) as the pads become leaky, the attractors
> become
> > >weaker.
> > >
> > >>
> > >> Watching the scope it appears to be 'locking' onto integral harmonics.
> > >> A square wave input might be converted to what looks like a square
> > >> wave which is amplitude modulated with 2 sine cycles for each 1/2
> > >> square cycle.  As you adjust Fc, all of a sudden, 2 sine cycles become
> > >> 3, etc.
> > >
> > >
> >
> > =========================================================
> > - Government: The other religion.
> > - The media's credibility should always be questioned.
> > - Lambs who lie down with lions are lunch.
> >
> > -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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> >
> >

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