[sdiy] What's going on in the M12 filter circuit?

[DJ Marmalade]

> There's a very good explanation here -
> http://www.musicsynthesizer.com/Circuitry/Multi-Function%20VCF.htm


Thanks for the info. I had this in my book but the last time I looked at it
I hadn't really tried to analyze the circuit, so I just pushed it aside.
So, from this I can extrapolate that the transfer functions for lowpass
filters. With a bit of effort I should be able to use the resistor values
and existing circuit to extrapolate functions for the other filter types. I
am clear on the cmos mux operation, that part of the circuit wasn't really
where my questions were. Nor do I care about other functions in the chip
such as VCAs or CV mixers.

Is it safe to assume that the very nature of filter circuits implies that
the cap connection for each pole provides an output from the pole?  If this
is true then I should be able to use ANY four pole lpf chip to build many
different varieties of filters.  Further, as I suspected, the resistor
values of the summing circuit are not unique to the 3372 but related to the
coefficients of each pole and would be the same, at least in relation to
each other, with ANY 4pole lpf chip?

Thanks
Daryl