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[iiwusynth-devel] Filter: solved
From: |
Markus Nentwig |
Subject: |
[iiwusynth-devel] Filter: solved |
Date: |
Mon, 01 Apr 2002 13:37:04 +0200 |
Hello,
good news: I have figured out the solution for the filter problem (sound
fond specs). As so often, it is all rather simple.
In a nutshell:
-> The Q mentioned in the specs is given in dB! Therefore, a soundfont Q
of 0 corresponds to an 'ordinary Q' of 1
-> A standard resonant low pass filter behaves exactly as described
regarding the Q: A Q of x dB results in a resonant peak of Q dB.
-> There is an additional rule: The total gain of the filter (linear)
has to be divided by Q (linear). Therefore, a Q of 10 dB lowers the
total filter gain by 5 dB, and adds a 10 dB resonant peak.
Some plotted curves for filter frequency responses, and more
explanation:
http://prdownloads.sourceforge.net/millisampler/SoundFont_FilterSpecs.pdf
A complete implementation with all equations, ready for implementation:
http://prdownloads.sourceforge.net/millisampler/Audio-EQ-Cookbook.txt
I'll try to find the time this afternoon to modify the existing filter
(shouldn't be too difficult).
Regards
Markus
PS: I hope that you don't have to turn your monitor in order to read the
file. Should I use .ps instead of .pdf?
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