AW: four-pole state variable filters

[Haible Juergen]

	>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. 

I vaguely remember a 4p SVF from EN. Think the denominator
had some specific (symmetrical ?) form, and there were two separate
damping factors introduced - but it's a quite cloudy memory.

JH.