[sdiy] filter resonance

[harrybissell]

Bzzzt.  (wrong)

Some filters have resonant feedback as you suggest... but most do not.
The State Variable filter has feedback from a circuit point that is not
always accessible (the BPF output) and the Moog ladder has feedback to
the other side of the input differential pair, normally never accessible.
The Sallen-Key (MS-20 et al) have a very different resonance control
(basically the gain of the amplifier)

Filters with cascaded integrator stages (like the CEM3320) could use the
technique you describe.

Bear in mind that you might use linearized photocell methods to do the
resonant control (see National Semi AN-20 "analog multiplier")

H^) harry



>On Thu, 11 Nov 2004 11:18:44 -0500 "john mahoney" <jmahoney at gate.net>
wrote.
>Is increasing a VCF's resonance the same as feeding more of its output
>back to its input? If so, then any filter can have voltage controlled
>resonance by adding a feedback loop with a VCA in it.
>
>Correct?
>--
>john
>