on Thursday, August 23, 2001 1:57 PM <
mate_stubb@...> wrote:
> I sent Paul a cool unique filter design several years ago, but he's
> undoubtedly forgotten about it by now. It came from a design paper in
> the SSM databook. It could be generated from the discrete quad OTA
> cell design that already powers the 440.
>
> It is....... ta da! a 4 pole state variable filter. Simultaneous LP,
> BP, HP, and notch, but with a steeper 4 pole response instead of the
> 2 pole response in standard designs. In addition, it has a unique
> double feedback path: one called Q and one called R.
>
> Q does what you would expect, while R separates the single peak into
> two peaks, and controls the spread between them. Allows for
> vocal/formant type sounds from a single state variable filter.
This sounds VERY cool - and unique! Separate VC of both Q and R would be
very interesting. Just thinking off the top of my head here (good luck),
would the R control be similar to the freq CV input when two 2-pole
multimode filters are hooked in serial, and the Fc CV input for #1 is being
reversed from the Fc CV input for #2?
George