[sdiy] filters, state variable in particular

[Aaron Lanterman]

On Sun, 18 Dec 2005, Paul Schreiber wrote:

> Not the fact the filter 'varies'. It has to do with the filter 'topology'. A 
> good example: Oberheim SEM filter.

I think the CS-80 uses two of them in cascade, one using the highpass 
output, and the other using lowpass. Paul sells an MOTM clone of it.

You can also do a digital version of the state variable filter - see Hal 
Chamberlin's book. It has some odd characteristics, like blowing up if 
implemented in floating point arithmetic if you set the cutoff too high, 
but it somehow is stable in finite precision arithmetic...

- Aaron

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