How to explain an analog state variable filter ..

[Tony Hardie-Bick]

On 13/10/11 10:32, Martin Naef wrote:
> On 13.10.2011 09:57, Marc Nostromo [M-.-n] wrote:
>> Pretty funny because I was just thinking about implementing a state
>> variable filter this morning. Truth is I'm looking for a generic/not too
>> expensive filter whose source code is easy to find (mostly for quick
>> tests and benchmarking). And that I wouldn't spend 4 days coding :)
>>
>> Would that be a good pick ? any other suggestion ?
>>
>> http://www.musicdsp.org/archive.php?classid=3#142
>
> That's the basic stuff, works smoothly if you understand the limits (e.g.
> stability as you approach Nyquist). Obviously, if you want character you need to
> look elsewhere (e.g. Tony's DSM).  [DFM!!!]

Actually, the SV filter has stability issues starting below fs/8, although the 
maximum stable frequency increases with decreasing resonance. There was a paper 
about this, with equations, which one can use to limit the resonance so the 
thing doesn't collapse into chaos (it's not musical).

Somewhere on a disk, I may even have it all written up, along with pseudocode.

Tony (HB)