[sdiy] Multimode filter topology

[David G. Dixon]

> You could use the patented T.R. approach and build up the circuit and play
> with it. Use digital pots to adjust things or whatever. Take notes on what
> patterns work and what don't.
> 
> Alternately CSound is a way to breadboard up stuff for testing without all
> that mucking about with copper and solder.

I was thinking that the easiest way to do it would be to rig up opamps as
gain blocks of alternating polarity with several input resistors in integer
ratios on a rotary switch (100k, 49.9k, 33.2k, 24.9k, 20k, 16.5k), feeding
another opamp summer.  Then, one could simply "dial in" the actual vector
{A,B,C,D,E}.