four-pole state variable filters

[Martin Czech]

> i'm interested in building a 4-pole, state variable filter - i know that
> designs for this circuit must be floating around, but i haven't been
> able to find any ... any clues?
> 
Is this just a mistake ? The usual SVF has 2 poles.  You can get any
even order response by cascading such  2-poles.

OTOH, if this is no mistake, well the "canonical" form is simply a
chain of 4 time variable (e.g. ota) integrators. Every integrator has
a feedback path to the first stage input. These feedback coefficients
controll the overall pole location. The input and each of the four
stages are  multiplied with a constant (pos , 0, negative) and summed,
the coeffcients give the zero locations. This is the output. This
arrangement gives all possible kinds of 4-pole output resonses.


m.c.