[Csnd-dev] FYI: ZDF Filters

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[Csnd-dev] FYI: ZDF Filters

Steven Yi
Hi All,

Just FYI, now that it's easy for me to develop with Visual Studio, I'm
starting work on translating those zero-delay feedback filters (the
ones by Will Pirkle that I had done UDO versions) to C in Csound.
I've just pushed the first commit which has the zdf_ladder.  A couple
things to note:

1. I'll be adding filters as I can.  When they get commited, and if
you're using the UDO version, it might be best to stop using the UDO

2. For zdf_ladder, I've adjusted the resonance mapping as I think I
had gotten it wrong earlier.  The resonance range is still 0 to 1.0,
but this now maps to Q range of 0.5 to 25.0.  The previous
calculations were off and could allow fairly catastrophic values as
resonance was getting closer and closer to 1.0.  As it is now, it will
get to 25.0 which self-oscillates and stop there.

3. I'm not 100% that the resonance mapping to Q is so great in terms
of its curve. I'm using Q = 1 / (2 * (1 - adjustedRes)).  (adjustedRes
goes from 0-0.98). It makes it hard to notice resonance changes until
it gets closer to 0.95 or so.  If anyone has suggestions here, it'd be
very much appreciated.

4. My plan is to add the filters, then work on documentation and
examples at end.

If there's anyone using develop branch, any tests/feedback on the
filters is always appreciated.