[sdiy] SSM2164 state-variable filter

[Ian Fritz]

>>Firstly, the resonance varies with cutoff frequency, being more
>>pronounced at higher frequencies (in fact, it'll oscillate at high
>>frequencies when it won't when you tun the cutoff down. Is this
>>normal? Do all SVF designs do this?

Q enhancement at high frequencies is a well known effect.  It comes from 
opamp phase shifts.  Find a good design and you will see the compensation 
built in.  Bernie Hutchins spent a lot of time looking at this, including 
analysis with the opamp poles included.

   Ian