Re: Filter algorithims
Re: Filter algorithims
- Subject: Re: Filter algorithims
- From: Nigel Redmon <email@hidden>
- Date: Sat, 20 Oct 2007 15:16:03 -0700
There's a huge amount of information on the web if you search. For
questions, try the music-dsp mailing list:
http://music.columbia.edu/cmc/music-dsp/
Some code is at a related website:
http://musicdsp.org/
Briefly, to get you pointing in a useful direction (there are many
kinds of filters you might have to wade through to figure out what
might be best suited for audio), the most-used audio filter is the
"biquad" (biquadratic), a two-pole, two-zero filter. Here's a little
info info on them, including a java applet that lets you move the
poles and zeros and see what they do. There's also a page on the
bilinear transform, which shows how the low pass filter is derived;
if you plug evaluate those equations given your frequency and Q
values and plug the results into one of the forms shown on the
"Biquad forms" page, you have a functioning filter. Robert Bristow-
Johnsons's cookbook page is a popular source, and he gives the
results of transforms on other basic filter types (don't be confused
by the fact his equations use sine and cosine and mine use tangent--
same results, different preferences in reducing the transform):
http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
Hal Chamberlin's digital version of the popular state-variable filter
common in analog synths is another often-used choice, particularly in
synthesizers. It's easier to control for synth use (sweeping the Fc
with an envelope, etc.):
http://www.earlevel.com/Digital Audio/StateVar.html
On Oct 19, 2007, at 10:57 PM, Kevin Dixon wrote:
I want to learn about filtering algorithims for Low Pass, High
Pass, and
Band Pass. Algorithims similar in nature to the LP filter
algorithim in
the FilterDemo are what i'm most interested in. They don't have to be
super-high performance, but good enough to execute in real time,
and learn
about them.
Any websites or books you would recommend to study this topic? Thanks!
-Kevin Dixon
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