[sdiy] Craig Anderton's Multiple Identity Filter

[Andrew Simper]

It amounts to pretty much the same thing as crossfading the outputs
(or even inputs with the inverted version!) of a couple of SVFs (or
even modified active Sallen Key type filters), apart from the obvious
differences in responses from the cascade structure vs two bi-quads.

I think most such "morphing" is a bit gimmicky, but it does sound cool
sweeping the notches away from the central resonant peak to create a
low pass / high pass / band pass out of a notch while the resonant
peak stays put.

Cheers,

Andy

On 27 October 2016 at 20:03, Olivier Gillet <ol.gillet at gmail.com> wrote:
>> I'm guessing you went this way. A 17-bit code gives you at least 8 resistor options for each of 5 inputs to the mixer (e.g. a 4051 for each one). Under uP control this gives fantastic flexibility and the problem becomes finding "useful" or "interesting" responses from a system which will include many duplicates and things that just aren't that good - including 30 from the 131,000+ possibilities suggests you did the required serious pruning!
>
> Pruning indeed! I prototyped a design in which each filter stage goes
> into a an attenuverter whose gain is controlled by a MCU. The goal was
> to allow continuous morphing from one response to the other, with each
> stage's "coefficient" being computed from 3 parameters: slope,
> response (LP to BP to HP) and "polarity" (LP becomes HP, BP becomes
> notch, HP becomes LP). And it's not that interesting, with many
> combinations of parameters sounding mild. I think you get more
> flexibility, for the same hardware budget, with two SVF with
> LP/Notch/HP/BP crossfading, and crossfading between serial/parallel
> routing.
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