[fluid-dev] A change to the IIR filter

[David Henningsson]

Hi,

A week ago I made a change to the IIR (Resonance/Cutoff) filter in order 
to fix ticket #82, it's in r415: 
http://sourceforge.net/apps/trac/fluidsynth/changeset/415/trunk/fluidsynth

A few things noted about this change:

1) It adds an floating point division in the inner loop in some cases. 
I'm not really happy about this (for performance reasons), and I've 
tried to work around this a little in r417, but any other suggestions 
are welcome.

2) Do you notice any changes in how things sound before and after, but 
it's at least theoretically possible that it does. Maybe it does in 
other listening environments and with other soundfonts than the ones 
I've tried with. Any notable change for you?

3) I'm not an IIR filter expert, and so I'm a little out on deep water 
here and I'm not completely sure this is the right way to fix it. If you 
happen to know any digital filter algorithm expert, feel free to ask 
him/her to review the code :-)

// David