SV: Re: SV: [sdiy] QVCO schemo up

[Anthony Bisset]

on/

my perspective oscillators would be much more musically useful if
they mirrored real systems rather than the limited and popular sine/tri/..

Is it possible this hopf/svf could allow a steady
sweep from sine all the way out to chaos/noise @freq?

Too couple non-linear chaotic systems and use them as the root for
non-chaotic systems was a magic sometime ago.

Without the need for serious temp comp, this circuit makes oscillator
building much easier for the less serious DIY'r like me.  I must thank you
to Ian for resurfacing this principle.

here's to more circuits that blur the line between
vco/vcf/vca/vgna

Pss i dislike just about every oscillator i've ever used and now generally
avoid them.  ringing filters, filtered noise, and physically model'd
systems are much better sounding, for me.  perhaps the art of synthesizers
is not matured as a cello still sounds much better imo.  from this
angle i feel new circuits and applications must be found if electrons are
going to sing like wood and cat.

-Anthony

/off


On Sat, 12 Nov 2005, Ian Fritz wrote:

> At 11:24 AM 11/12/05, Don Tillman wrote:
>
> >Maybe it should be an actual Hopf Bifurcation device?
> >
> >Ian, would you say that your approximation of the original equations
> >has changed the circuit from being an actual Hopf Bifurcation device
> >to a State Variable Filter oscillator?
>
> Well ... interesting question.  First understand that the Hopf bifurcation
> is a *general* type of bifurcation that causes a system to go from a steady
> state at a fixed point (no time dependence) to a stable limit cycle
> oscillation (usually circular, I think).  So the equation pair I started
> with in polar coordinates is just *one* simple example of a Hopf
> bifurcation.  In my system, if I add extra damping then it will  start to
> oscillate as this damping is decreased beyond a certain point.  I believe
> this is still a Hopf bifurcation, although it would take me some work to
> prove it.  (There are general mathematical criteria for the Hopf bifurcation.)
>
> When I first hooked the quad osc system up, I used the building blocks I am
> now using to develop higher order chaos, namely a *damped* integrator
> followed by the zener nonlinear circuit.  This setup showed a Hopf
> bifurcation as I decreased the damping.  After that, I took out the
> integrator damping and so now the circuit always just oscillates. So there
> is no longer a parameter available to actually see the bifurcation occur,
> but I think it is fair to say that the oscillation comes from the Hopf
> bifurcation.  Not particularily useful, just an interesting fact, and a
> tie-in to general nonlinear dynamics theory.
>
>
> >Why do a Hofp Bifurcation device at all?  Maybe it would be musically
> >useful to disturb it from its oscillating state.  Any thoughts?
>
> No reason at all.   :-)   I was learning about the simple prototype example
> and was curious as to what an electronic implementation would be like.  So
> first I converted to cartesian coordinates, then I simplified the system
> equations, then I saw I could build the system with building blocks I
> already had built, sitting on an experimental board.  It only took a couple
> of minutes to hook up.  Then I found that I could leave out one of the two
> nonlinear circuits.  What a way to get a standard, well known result,
> eh?  If I had thought more about what I was doing I might have realized
> that I would end up with a state-variable system, but I just plowed ahead
> because I had the circuit blocks already built.
>
>
> >So, the State Variable Filter oscillator is well known.  The question
> >is, does Ian's variation of the stabilizer with the zeners provide
> >better (or otherwise more musical) performance?  I dunno.
>
> Actually my implementation turns out to be almost exactly the same as the
> Burwen circuit in the AD handbook.  I don't think the details of the
> nonlinearity matter much -- all you need is for the (antisymmetric)
> transfer function to cross zero with a negative slope at a finite input level.
>
>
> >One of the problems with filter-feedback oscillators is that they take
> >a while to stabilize.  So, for instance, I would be interested in
> >seing how Ian's circuit reacts to a large sudden step change in
> >frequency.
>
> Right. We looked at that yesterday.  Both my measurements and Harry's
> simulation show that the system takes a couple of hundred cycles to come to
> equilibrium at power up.  However, once the system is running it seems that
> the frequency can be changed instantaneously.  This is because at the new
> frequency the two signals still have the same phase relation as before, so
> all you need is for the integrators to ramp at a different rate.  This is
> instantaneous.
>
>    Ian
>
>