Vadim's book "The Art of VA Filter Design" is here as a (free-to-distribute) PDF,
https://www.native-instruments.com/fileadmin/ni_media/downloads/pdf/VAFilterDesign_1.1.1.pdf It's an excellent resource (to put it mildly). On Sat, Feb 3, 2018 at 7:49 AM, Dario Sanfilippo <sanfilippo.da...@gmail.com > wrote: > Thanks for the links, Steven! > > Vadim, what is the title of your book? We may have it here at uni. > > Hi, Robert. I'm working on some time-domain feature-extraction algorithms > based on adaptive mechanisms. A couple of years ago, I implemented a > spectral tendency estimator where the cutoff of a crossover (1p1z filters) > is piloted by the RMS imbalance of the two spectra coming out of the same > crossover. Essentially, a negative feedback loop for the imbalance pushes > the cutoff towards the predominant spectrum until there's a "dynamical > equilibrium" point which is the estimated tendency. > > A recent extension to that algorithm was to add a lowpass filter within > the loop, at the top of the chain, as shown in this diagram: > https://www.dropbox.com/s/a1dtk0ri64acssc/lowest%20partial.jpg?dl=0. > (Some parts necessary to avoid the algorithm from entering attractors have > been omitted.) > > If the same spectral imbalance also pilots the cutoff of the lowpass > filter, we have a nested positive (the lowpass strengthens the imbalance > which pushes the cutoff towards the same direction) and negative (the > crossover's dynamical equilibrium point) feedback loop. So it is a > recursive function which removes partials from top to bottom until there is > nothing left to remove except the lowest partial in the spectrum. > > The order and type of the lowpass (I've tried 1p1z ones, cascading up to > four of them), I believe, is what determines the SNR in the system, so what > the minimum amplitude of the bottom partial should be to be considered > signal or not. Large transition bands in the lowpass will affect the result > as the top partials which are not fully attenuated will affect the > equilibrium point. Since elliptic filters have narrow transition bands at > low orders, I thought that they could have given more accurate results, > although the ripples in the passing band would also affect the SNR of the > system. > > Perhaps using Butterworth filters could be best as the flat passing band > could make it easier to model a "threshold/sensitivity" parameter. With > that regard, I should also have a look at fractional order filters. (I've > quickly tried by linearly interpolating between filters of different orders > but I doubt that that's the precise way to go.) > > Of course, an FFT algorithm would perhaps be easier to model, though this > time-domain one should be CPU-less-expensive, not limited to the bin > resolution, and would provide a continuous estimation not limited to the > FFT period. > > I've tested the algorithm and it seems to have a convincing behaviour for > most test signals, though it is not too accurate in some specific cases. > > Any comment on how to possibly improve that is welcome. > > Thanks, > Dario > > > Dario Sanfilippo - Research, Teaching and Performance > Reid School of Music, Edinburgh University > +447492094358 <+44%207492%20094358> > http://twitter.com/dariosanfilippo > http://dariosanfilippo.tumblr.com > > On 3 February 2018 at 08:01, robert bristow-johnson < > r...@audioimagination.com> wrote: > >> i'm sorta curious as to what a musical application is for elliptical >> filters that cannot be better done with butterworth or, perhaps, type 2 >> tchebyshev filters? the latter two are a bit easier to derive closed-form >> solutions for the coefficients. >> >> whatever. (but i am curious.) >> >> -- >> >> r b-j r...@audioimagination.com >> >> "Imagination is more important than knowledge." >> >> >> >> ---------------------------- Original Message ---------------------------- >> Subject: Re: [music-dsp] Elliptic filters coefficients >> From: "Dario Sanfilippo" <sanfilippo.da...@gmail.com> >> Date: Fri, February 2, 2018 6:37 am >> To: music-dsp@music.columbia.edu >> ------------------------------------------------------------ >> -------------- >> >> >> > Thanks, Vadim. >> > >> > I don't have a math background so it might take me longer than I wished >> to >> > obtain the coefficients that way, but it's probably time to learn it. >> With >> > that regard, would you have a particularly good online resource that >> you'd >> > suggest for pole-zero analysis and filter design? >> > >> > Thanks to you too, Shannon. >> > >> > Best, >> > Dario >> > >> > On 1 February 2018 at 11:16, Vadim Zavalishin < >> > vadim.zavalis...@native-instruments.de> wrote: >> > >> >> Hmm, the Wikipedia article on elliptic filters has a formula to >> calculate >> >> the poles and further references the Wikipedia article on elliptic >> rational >> >> functions which effectively contains the formula for the zeros. >> Obtaining >> >> the coefficients from poles and zeros should be straightforward. >> >> >> >> Regards, >> >> Vadim >> >> >> >> >> >> On 01-Feb-18 12:00, Dario Sanfilippo wrote: >> >> >> >>> Hello, everybody. >> >>> >> >>> I was wondering if you could please help me with elliptic filters. I >> had >> >>> a look online and I couldn't find the equations to calculate the >> >>> coefficients. >> >>> >> >>> Has any of you worked on that? >> >>> >> >>> Thanks, >> >>> Dario >> >>> >> >>> >> >>> _______________________________________________ >> >>> dupswapdrop: music-dsp mailing list >> >>> music-dsp@music.columbia.edu >> >>> https://lists.columbia.edu/mailman/listinfo/music-dsp >> >>> >> >>> >> >> -- >> >> Vadim Zavalishin >> >> Reaktor Application Architect >> >> Native Instruments GmbH >> >> +49-30-611035-0 >> >> >> >> www.native-instruments.com >> >> _______________________________________________ >> >> dupswapdrop: music-dsp mailing list >> >> music-dsp@music.columbia.edu >> >> https://lists.columbia.edu/mailman/listinfo/music-dsp >> >> >> >> >> > _______________________________________________ >> > dupswapdrop: music-dsp mailing list >> > music-dsp@music.columbia.edu >> > https://lists.columbia.edu/mailman/listinfo/music-dsp >> >> >> >> _______________________________________________ >> dupswapdrop: music-dsp mailing list >> music-dsp@music.columbia.edu >> https://lists.columbia.edu/mailman/listinfo/music-dsp >> > > > _______________________________________________ > dupswapdrop: music-dsp mailing list > music-dsp@music.columbia.edu > https://lists.columbia.edu/mailman/listinfo/music-dsp >
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