[sdiy] Resonance control taper ?

[cheater cheater]

They're all good oscillators Neil

On Mon, Sep 12, 2022 at 10:22 AM Neil Johnson via Synth-diy
<synth-diy at synth-diy.org> wrote:
>
> Hi Roman,
>
> > Neil Johnson via Synth-diy pisze:
> > > I *think* he means that with an SVF you can dial in a very high Q and
> > > the filter will not oscillate, whereas other filter structures, such as
> > > ladder, at high Q can randomly burst into oscillation when you least
> > > expect it, and so you either limit the maximum Q or you need a very fine
> > > Q control as you get close to that point.
>
> Roman Sowa wrote:
> > Maybe I was doing something wrong all those years, but every SVF I made
> > was oscillating without much effort.
>
> Ah, what I meant by "high Q" is a very high Q but where the filter is
> still a filter, just ringing for a long time (possibly seconds).  I
> agree that the SVF topology is very easy to make an oscillator, but to
> make a good oscillator needs careful attention to the AGC loop to
> minimise injection of modulation artifacts.  The oscillator in the
> Audio Precision System One, for example, is an SVF and has quite a
> complicated AGC to (a) get the filter level to the right amount
> quickly, and (b) minimise distortion introduced by rapid amplitude
> changes.  The "leveler" circuit is an entire schematic page all to
> itself.
>
> Cheers
> Neil
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