2nd-order allpass VCFs?

Martin Czech martin.czech at intermetall.de
Tue Nov 23 08:39:18 CET 1999


:::Hi all:
:::
:::Has anyone here ever constructed a voltage-controlled 2nd-order allpass
:::filter? I'm not even sure how this would be done - a modification of the
:::state-variable filter, perhaps? 

Yes, the state variable can do any second order response.  hp and lp
gives notch, notch and bp gives ap.  In a serial arrangement you might
only need the notch. (from my head).

The big advantage is that poles now can get complex, this changes the
speepness of the phase rollof.

Even in the case of ap you can hear the poles, and the severe phase
distortion, a good illustration of the fact the magnitude allone is not
sufficient to jugde about sound.

m.c.




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