[sdiy] 3 Pole state-variable filters

[jhaible]

> I'm currently working on an 18dB state-variable filter (LP/BP/HP at the
> SAME time, unlike the Formant).  The maths gets a bit hairy,

>Its not too bad if you're familiar with s-plane math.

3 poles for HP and LP make sense. I think 3 poles on BP would mean
you spend one pair for the BP function, and then decide whether to
steepen the upper or the lower slope (i.e. adding a real pole LPF or HPF).
Or is there a way to "distribute" 3 poles equally on both slopes of a
BPF function ?

JH.