AW: Nonlinear Oscillators?

[Kimmo Koli]

Well, 
I remember a conference paper in ISCAS´96 in Atlanta where if I remember
correctly Edgar Sanchez-Sinencios's research group had designed a chaotic
oscillator based on a state-variable filter. It had the normal
negative feedback path for Q-tuning but also a comparator with hysteresis
as an additional feedback. That would be an easy addition to a standard
analog VCF. Probably with suitable feedback value it could add some kind
of a chaotich sub-osc to an normal synth sound. And also this chaotic VCF
could be used as a VCO.  

Unfortunately I'm not reading my emails at least for a week due to summer
holidays. So if You want to ask someting more about this, the answering 
may take some time....

Best regards, Kimmo Koli

On Fri, 10 Jul 1998, Haible Juergen wrote:
> 
> >Also, has anyone tried filter FM, with the modulating signal being the
> >output of the filter that is run through a nonlinear element (full-wave
> >rectifier, clipper, suboctave divider, etc.)?  Both the allpass-FM and
> >filter-FM methods would allow any signal to be run through the circuit,
> >not just an oscillator.  I wouldn't think that either of these methods
> >would produce the octave-jumping effect I am after, but I could be very
> >much wrong.  
> 
> I didn't get octave jumps, but the method is extremely rewarding,
> nevertheless.
> On my CS-50, I have the main audio output plugged into the
> "external in" all the time, so the audio output is available for
> all modulations that the LFO ("sub oscillator" in Yamaha speak)
> could do. I use it regularly to modulate the filter, and also the VCA,
> and it is great to create a complex attack phase on an otherwise
> boring sound. For example, the "Flute" preset becomes a trumpet
> sound that rivals the VL7 in expression (and leaves it far behind
> in terms of warmth), just with a little VCA modulation from the audio
> output.
> Larger modulation depths cause chaotic sounds, but the interesting
> region is just "close to the edge". BTW, though I never exactly
> analyzed this behaviour, but if memory serves the external input
> of the CS-50 is ac coupled and I have it set to mic level (the trimpot
> is a little hard to move on mine), so ther is probably some linear and
> nonlinear processing in the feedback loop.
> Might be interesting to evaluate this further on the Modular.
> 
> JH.
>  
> 

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   Kimmo Koli                         Helsinki University of Technology 
   kimmo at ecdl.hut.fi                  Electronic Circuit Design Laboratory
   http://www.ecdl.hut.fi/~kimmo      P.O.Box 3000
   Tel:  +358 9 451 2273              FIN-02015 HUT
   Fax:  +358 9 451 2269              Finland 
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