Hello!
I'm looking to build a couple of parametric EQs with 4 to 6 poles. At the moment I'm looking at the biquad equations in the help file and can't make heads or tails of them. I can't find anything helpful on the internet either on how those equations relate to the frequency response of the filter. I'm getting into FIR filters but am equally confused. Any suggestions? Has anyone else built parametric EQ modules for me to tinker with?
Thanks! Phil
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Hi Phillip,
Phillip Stearns wrote:
I'm looking to build a couple of parametric EQs with 4 to 6 poles. At the moment I'm looking at the biquad equations in the help file and can't make heads or tails of them.
Try the [lowpass]/[bandpass]/[highpass] objects from the GGEE lib. They make setting the coefficients much easier. I simply stacked instances of [biquad~] together if I needed sharped cutoff. Hope that helps.
derek
looking to build a couple of parametric EQs with 4 to 6 poles. At the moment I'm looking at the biquad equations in the help file and can't make heads or tails of them. I can't find anything helpful on the internet either on how those equations relate to the frequency response of the filter.
assuming youve used RBJ's variables, as in http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt the response for a particular frequency is sqrt(pow(($b0+$b1*cos($w)+$b2*cos(2*$w)),2)+pow(($b1*sin($w)+$b2*sin(2*$w)),2))/sqrt(pow(($a0+$a1*cos($w)+$a2*cos(2*$w)),2)+pow(($a1*sin($w)+$a2*sin(2*$w)),2))
Has anyone else built parametric EQ modules for me to tinker with?
for pd, theres a Tk version at http://cvs.sourceforge.net/viewcvs.py/pure-data/extensions/gui/ix/filter.wid... and C versions at http://cvs.sourceforge.net/viewcvs.py/pure-data/externals/ggee/filters/ . if you make an abstraction-based version of biquad param generators, let us know!
On Fri, 23 Dec 2005, c wrote:
sqrt(pow(($b0+$b1*cos($w)+$b2*cos(2*$w)),2)+pow(($b1*sin($w)+$b2*sin(2*$w)),2))/sqrt(pow(($a0+$a1*cos($w)+$a2*cos(2*$w)),2)+pow(($a1*sin($w)+$a2*sin(2*$w)),2))
This scary-looking formula is less scary reformatted like this:
sqrt(pow(($b0+$b1*cos($w)+$b2*cos(2*$w)),2) +pow(( $b1*sin($w)+$b2*sin(2*$w)),2))/ sqrt(pow(($a0+$a1*cos($w)+$a2*cos(2*$w)),2) +pow(( $a1*sin($w)+$a2*sin(2*$w)),2))
And then using slightly more advanced math concepts it can be further simplified like this:
norm(($b0,0)+($b1,$b2)*M)/ norm(($a0,0)+($a1,$a2)*M) where M is the matrix (cos($w), cos(2*$w); sin($w), sin(2*$w))
_ _ __ ___ _____ ________ _____________ _____________________ ... | Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju | Freelance Digital Arts Engineer, Montréal QC Canada
A simple (I think) example is in 3.audio.examples/H11.shelving.pd and 3.audio.examples/H12.peaking.pd in the Pd distribution... explained further in http://crca.ucsd.edu/~msp/techniques/ (chapter 8, filters. A simple (I think) example is in 3.audio.examples/H11.shelving.pd and 3.audio.examples/H12.peaking.pd in the Pd distribution... explained further in http://crca.ucsd.edu/~msp/techniques/ (chapter 8, filters).
cheers Miller
On Fri, Dec 23, 2005 at 08:24:55AM -0800, Phillip Stearns wrote:
I'm looking to build a couple of parametric EQs with 4 to 6 poles. At the moment I'm looking at the biquad equations in the help file and can't make heads or tails of them. I can't find anything helpful on the internet either on how those equations relate to the frequency response of the filter. I'm getting into FIR filters but am equally confused. Any suggestions? Has anyone else built parametric EQ modules for me to tinker with?
Thanks! Phil
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c -
derek holzer -
Mathieu Bouchard -
Miller Puckette -
Phillip Stearns