AW: [sdiy] filters with independent resonance 'location'

[Czech Martin]

The usuall resonance is obtained via feedback.
In order to get a "hump" in frequency response, 
the phase shift of the filter must be large enough,
and this is usually the case near the cutoff frequency.

Of course, a state var (e.g.) filter allows for all possible
pole and zero locations and therefore all possible
filter shapes. But this is not the usuall thing.

I remember a E.N. filter, I think it was a Tchebycheff
6 pole design with deliberately large passband wiggle,
more then 6dB or so. Since such filters are not usual,
there exist no design tables, but the pole configuration
for all such designs is pretty easy to figure out.
This filter used three state vars, giving three locked
"humps", AFAIR.

If you have a couple of state vars in your synth plus
a mixer with input inversion switches, you can build 
this very quickly without further soldering.

m.c.

> -----Ursprüngliche Nachricht-----
> Von: Jeffrey Pontius [mailto:jpont at stat.ksu.edu]
> Gesendet: Dienstag, 25. September 2001 14:56
> An: synth-diy at dropmix.xs4all.nl
> Betreff: [sdiy] filters with independent resonance 'location'
> 
> 
> In general, a typical lowpass or highpass filter has the resonance set
> around the cutoff frequency.  Are there filters available, and if not
> available could one be reasonable constructed, that would allow the
> resonance 'location' to be set independently of the cutoff frequency?
> 
> This is certainly not a new idea, but I have not seen or read 
> about such a
> filter.
> Thanks, Jeff
>