I'll check out the settings. As for running this, its a script, you
can just run it on the Terminal. On GNU/Linux, it should just work.
On Mac OS X, you'll probably need to have run it like this:
/usr/bin/wish filterview.tcl
.hc
On Feb 7, 2011, at 11:20 PM, Mike Moser-Booth wrote:
I don't really know how to test this and I don't really know tcl,
but I tried looking at the code to see if I could make some sense of
it anyway, because why the hell not. ;-) Anyway, the only part I
really understood was the calculation of the coefficients, and I
noticed something wrong. You are calculating alpha for bandwidth
instead of Q. I'm guessing you're just borrowing what is in the ggee
externals (given the code's comments), because it's done the same
way there, but it's not really conventional for a lowpass filter.
That's really more for bandpass, notch, and peaking filters. Using Q
is also a simpler calculation: alpha = sin(omega)/(2*Q). With Q set
to .7071 (or -3 dBfs), you have a filter with no resonance, which
makes sense because the cutoff frequency for a lowpass filter is
defined as the frequency where the response falls be 3 dB. This is
also how Max's [filtergraph~] works.It's all defined here in Robert Bristow-Johnson's Cookbook:
http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
The ggee externals, as far as I can tell, are all based on this
cookbook, though with mistakes like using BW instead of Q.Hope that helps, .mmb
On Mon, Feb 7, 2011 at 10:03 PM, Hans-Christoph Steiner
hans@at.or.at wrote:On Feb 7, 2011, at 8:35 PM, Spencer Russell wrote:
On Sun, Feb 6, 2011 at 11:15 PM, Mathieu Bouchard
matju@artengine.ca wrote: On Sun, 6 Feb 2011, Spencer Russell wrote:[1] gives the magnitude frequency response given the biquad coefficents, and it linked to from several places around the net. Is this the sort of thing you're looking for? [1] http://bit.ly/eFck4j
This link got me directly to :
USB complete: everything you need to develop custom USB peripherals Par Jan Axelson Chapitre 12 Page 364
and nothing else. (??)
Whoops, I meant to send this: http://bit.ly/gUCBu4. Sorry.
Here he's basically just taken the transfer function of a biquad and made the z = exp(j*w/Fs) as Mike suggested, followed by taking the magnitude and log-scaling for dB, but he's done the algebraic legwork. Just note that w (lower-case omega) is 2*pi*f and you should be good to go. He's also done some trig-substitution for more numerical precision.
I'm making good progress, but now am getting lost in the filter math
meeting the pixel math. Can someone mathy check my math? Or even
try it out?https://github.com/pd-projects/filterview
.hc
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