[sdiy] Multimode filter topology

[David G. Dixon]

> This topic was discussed at some length a few months ago under the thread
> "XPander VCF" I think.

Thanks, George.  I went back and reread the entire thread, and it was all
there, to be sure.  I was just too much of a newbie to understand much of
what was being said at the time.
 
One thing I noticed is that Andy never answered the questions about exactly
which stage factors he assumed to generate some of his notch plots, and
whether he changed capacitor values to get the various notches and peaks
within one mode.  I'd still like to know the answer, but I'm going to
generate my own plots in the meantime.