[sdiy] Filter Musings

[JH.]

>I was going through a variety of schematics for ladder filters (Moog and the diode spin-offs) and was wondering what would happen 
>if you put two or more >of the filter "cores" in parallel in the circuit. Would it just be like having multiple filters controlled 
>by the same CVs, or would it add poles to the filter?

Excepting the trivial case of two identical filters, you will get a more complex behaviour than with a single filter.
Two 4-pole LPFs in parallel form an 8-pole filter indeed. But you also get zeroes, so there will be no 48dB/Oct slope.

Serial connection of two 4pole LPFs without zeroes means *multiplication* of the transfer functions -> poles only -> 48dB/Oct slope

Parallel connection of two 4pole LPFs without zeroes means *addition* of the transfer functions -> finding the common denominator to 
perform the addition means you get "jw"-terms into the numerator -> zeroes are created.

JH.