[sdiy] 4 Pole state-variable filters

[Sowa Roman]

I have VCF similar to what you described and must admit that
2 cascaded 2-pole filters sound really good, and can deliver much
more fun that single 4 pole filter.
Mine are based on SSM2164 quad VCA. 2 VCAs for filter, one
for Q control, one N/C. Best effects give cascading different types
of outputs, e.g. LP to HP etc with detuning the filters.
see for yourself:
http://romcio.multimania.com/vcf.html
updatet recently with schematics
some sound of it:
http://romcio.multimania.com/m_samples/steps.mp3
not the best example of VCF alone, but the best I have there now.

Roman

""-----Original Message-----
""From: Theo [mailto:t.hogers at home.nl]
""Sent: Sunday, February 10, 2002 8:43 PM
""To: Grant Richter; The Proteus; synth-diy at dropmix.xs4all.nl
""Subject: Re: [sdiy] 4 Pole state-variable filters
""
""
""I toyed with 4pole statevariable filters a while ago.
""The filter sounded good, but you need to tweak the feedback level
""for the HP function relative to the resonance and cutoff setting.
""Someone from this list send me a circuit from the EN later on.
""Basically this was the same circuit as I had come up with,
""and it had the same feedback level problem.
""(The EN circuit used OTAs, mine used diode bridges)
""Bit of a disappointment as I expected a genius solution for the
""problematic feedback behavior from the mythical EN.
""A possible solution would be to make the resonance voltage controlled
""and use the resonance and cutoff CV to alter the HP feedback level.
""(HP feedback level is probably not the proper name,
""but hope you understand anyway)
""
""Cascading two 12dB filters gave better results,
""so the 24dB statevariable was dropped.
""At this point I experiment with two cascaded filters,
""but the resonance loop goes from the BP output of the second filter
""to the input of the first filter.
""
<snip>


---------------------------------------------------------
This message has been scanned for viruses by MIMESweeper.

Wiadomosc zostala sprawdzona pod katem wirusow przez
oprogramowanie MIMESweeper.