hi all, I've been working on filter patches for my courses and I'm still failing ti get biquad coeficients from the [vcf~] code. Maybe anyone out there could help?
I wanted this to plot the frequency response in realtime... the [vcf~] filters aren't in the audio Audio-EQ-Cookbook, and the code looks a bit too complicated thanks 2014-05-26 10:23 GMT-03:00 Joe White <white.j...@gmail.com>: > Ahh yes of course thanks Frank! > > Have you guys checked out this paper on 'High-Order Digital Parametric > Equalizer Design <http://www.aes.org/e-lib/browse.cfm?elib=13397>'? > Apparently it reduces the need to cascade filter implementations to achieve > high orders. > > Cheers, > Joe > > > On 24 May 2014 09:53, Frank Barknecht <f...@footils.org> wrote: > >> Hi Joe, >> >> versions of these calculations without [expr] are also part of the >> rj-library as u_lowpass, u_lowpassq etc. These have been taken straight >> from the Audio-EQ-Cookbook. >> >> Ciao >> -- >> Frank >> >> On Fri, May 23, 2014 at 12:06:45PM +0100, Joe White wrote: >> > Thanks for the abstractions Chris. Am I correct in thinking the >> licensing >> > issues for [expr] have been resolved now? >> > >> > Cheers, >> > Joe >> > >> > >> > On 21 May 2014 23:22, Chris Clepper <cgclep...@gmail.com> wrote: >> > >> > > On Wed, May 21, 2014 at 5:31 PM, Joe White <white.j...@gmail.com> >> wrote: >> > > >> > >> >> > >> >> > >> Is it intentional to not a bank of go-to filters? [biquad~] is the >> next >> > >> one I would go to, but generating your own coefficients isn't >> that... err.. >> > >> efficient when you're wanting some that just 'works' :) >> > >> >> > >> >> > > Attached are a set of abstractions wrapping most of the 'Audio EQ >> > > Cookbook' formulae around biquad~. It would be nice for Pd to include >> > > something like this. >> > > >> > > The only drawback to [biquad~] is it doesn't take audio rate >> coefficients. >> > > There are of course externals that do audio rate for cutoff, Q, etc. >> > > >> > > Chris >> > > >> > > >> > >> >> > >> >> > >> On 21 May 2014 17:31, Miller Puckette <m...@ucsd.edu> wrote: >> > >> >> > >>> Hi Joe - >> > >>> >> > >>> That code is an approximation that works well for low cutoff >> > >>> frequencies but badly for high ones. (I should probably warn >> > >>> about this in the help window... that'll go on my dolist) >> > >>> >> > >>> cheers >> > >>> M >> > >>> >> > >>> >> > >>> On Fri, May 16, 2014 at 12:58:31PM +0100, Joe White wrote: >> > >>> > Hi, >> > >>> > >> > >>> > I've been looking at the [lop~] implementation (Pd-0.45-4) and >> noticed >> > >>> > something that seem weird to me. >> > >>> > >> > >>> > In d_filter, line 176: >> > >>> > >> > >>> > static void siglop_ft1(t_siglop *x, t_floatarg f) >> > >>> > { >> > >>> > if (f < 0) f = 0; >> > >>> > x->x_hz = f; >> > >>> > x->x_ctl->c_coef = f * (2 * 3.14159) / x->x_sr; >> > >>> > if (x->x_ctl->c_coef > 1) >> > >>> > x->x_ctl->c_coef = 1; >> > >>> > else if (x->x_ctl->c_coef < 0) >> > >>> > x->x_ctl->c_coef = 0; >> > >>> > } >> > >>> > >> > >>> > >> > >>> > Is it correct that for: >> > >>> > >> > >>> > y[n] = x[n] * a + y[n-1] * b >> > >>> > >> > >>> > *a = 2π * Fc / Fs* >> > >>> > b = 1.0 - a >> > >>> > >> > >>> > where Fc is the cut-off frequency and Fs the sampling frequency. >> > >>> > >> > >>> > I appreciate the a coefficient is bounded afterwards but wouldn't >> that >> > >>> mean >> > >>> > that Fc values greater than Fs / 2π will have no impact on the >> sound >> > >>> being >> > >>> > processed. >> > >>> > >> > >>> > For example if Fs is 44100, then Fc values above ~7020Hz will not >> > >>> affect >> > >>> > the filter. >> > >>> > >> > >>> > Have I missed something crucial or could this a bug in the code? >> > >>> > >> > >>> > The simple IIR filter described in >> > >>> > http://en.wikipedia.org/wiki/Low-pass_filter suggests that the >> actual >> > >>> > coefficient calculation should be more like: >> > >>> > >> > >>> > a = 2π*Fc / (2π*Fc + Fs) >> > >>> > >> > >>> > Looking forward to understand this more! >> > >>> > >> > >>> > Cheers, >> > >>> > Joe >> > >>> > >> > >>> > -- >> > >>> > Follow me on Twitter @diplojocus >> > >>> >> > >>> > _______________________________________________ >> > >>> > Pd-list@lists.iem.at mailing list >> > >>> > UNSUBSCRIBE and account-management -> >> > >>> http://lists.puredata.info/listinfo/pd-list >> > >>> >> > >>> >> > >> >> > >> >> > >> -- >> > >> Follow me on Twitter @diplojocus >> > >> >> > >> _______________________________________________ >> > >> Pd-list@lists.iem.at mailing list >> > >> UNSUBSCRIBE and account-management -> >> > >> http://lists.puredata.info/listinfo/pd-list >> > >> >> > >> >> > > >> > >> > >> > -- >> > Follow me on Twitter @diplojocus >> >> > _______________________________________________ >> > Pd-list@lists.iem.at mailing list >> > UNSUBSCRIBE and account-management -> >> http://lists.puredata.info/listinfo/pd-list >> >> > > > -- > Follow me on Twitter @diplojocus > > _______________________________________________ > Pd-list@lists.iem.at mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > >
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