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[fluid-dev] A change to the IIR filter

From: David Henningsson
Subject: [fluid-dev] A change to the IIR filter
Date: Sun, 03 Apr 2011 11:38:44 +0200
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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

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