Pd-list March 2010

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152 participants
270 discussions

Re: [PD] tabread4~ "broken" interpolation algorithm - was Re:, Max Smoother Audio than Pd?
by Matteo Sisti Sette 30 Mar '10

30 Mar '10

Is it really possible to express a cubic interpolator (such as Lagrange or Hermite, i.e. such as tabread4 or tabread4c) in terms of impulse response? Is it equivalent to a convolution? That is to ask: is it linear??? Or is that an approximation? -- Matteo Sisti Sette matteosistisette(a)gmail.com http://www.matteosistisette.com

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glitches
by Vilson Vieira 30 Mar '10

30 Mar '10

Hi guys, anyone knows some patch to do glitch video? I found this http://blog.minzky.com/2008/10/27/puredata-with-gem-and-analog-audiovideomi… no source. Thanks. -- Vilson Vieira vilson(a)void.cc personal ~ http://automata.cc collective ~ http://musa.cc

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tabread4~ "broken" interpolation algorithm - was Re: Max Smoother Audio than Pd?
by Mathieu Bouchard 30 Mar '10

30 Mar '10

> I checked it out (not read the _whole_ thread to the end) but, In what > way can the current tabread4~ interpolation, which is discontinuous even > in its 1st derivative, be superior to true cubic interpolation? Even at > transpositions near to zero, I can't see what's the advantage, nor what > it is supposed to minimize. both are truly cubic interpolations. IIRC, one kind of cubic interpolation is designed to go through all four points, and the other kind is designed to be pieced with other cubic interpolations, and Miller confused the two and left the bug there. _ _ __ ___ _____ ________ _____________ _____________________ ... | Mathieu Bouchard, Montréal, Québec. téléphone: +1.514.383.3801

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Re: [PD] tabread4~ "broken" interpolation algorithm - was Re:, Max Smoother Audio than Pd?
by Matteo Sisti Sette 30 Mar '10

30 Mar '10

> So to me > it still remains unclear in what aspect [tabread4~] is superior > to [tabread4c~], from both a theoretical and from an empirical > perspective. The answer may be here: http://www.aes.org/e-lib/browse.cfm?elib=8151 Btw does anybody have access to that article? "The analysis reveals an interesting performance trade-off between signal-to-noise ratio and passband flatness." So since it seems quite obvious that discontinuities (tabread4) generate more high-frequency noise (and assuming that is the most relevant source of noise), the only aspect where tabread4 can be superior may be "passband flatness". Indeed, intuitively it seems plausible: passband flatness means that the low-frequency part of the signal is more close to the "original" (the ideal perfectly interpolated signal); and I do expect that an interpolator that doesn't try to match first derivatives is less likely to do crazy oscillations. It would be interesting to see a zoom-in of the low frequency part of Charles Henry's graph (the ripples in the flat zone). However, even in presence of a tradeoff that makes some sense (i.e. each of the two choices has advantages and disadvantages), it seems to me that for audio applications the generated high-frequency noise due to discontinuities should be _hugely_ worse than the passband-non-flatness. I'd really like to see and hear an example of a case where this isn't true, that is, where tabread4 gives better results than tabread4c. This other article seems to contain an answer: http://www.akademiai.com/content/r0192mk0908k31k3/ http://www.akademiai.com/content/r0192mk0908k31k3/fulltext.pdf?page=1 "The aim of this paper is to give a positive answer for a problem [...]: Do there exist a system of nodes and function class for which the Lagrange process is better than the Hermite-Fej6r one?" If anybody has access and can share it that would be great. Now regarding Matt's words: > I have read that the Lagrange interpolators have better stopband > attenuation and Hermites have flatter passband response, but I'm not > sure this is true Is it possible that it is exactly viceversa? By the way thanks again Matt (and everybody else who contributed to this thread) for the didactic effort and the links. -- Matteo Sisti Sette matteosistisette(a)gmail.com http://www.matteosistisette.com

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Re: [PD] tabread4~ "broken" interpolation algorithm - was Re: Max Smoother Audio than Pd?
by Matt Barber 30 Mar '10

30 Mar '10

> >> I checked it out (not read the _whole_ thread to the end) but, In what >> way can the current tabread4~ interpolation, which is discontinuous even >> in its 1st derivative, be superior to true cubic interpolation? Even at >> transpositions near to zero, I can't see what's the advantage, nor what >> it is supposed to minimize. > > both are truly cubic interpolations. > > IIRC, one kind of cubic interpolation is designed to go through all four > points, and the other kind is designed to be pieced with other cubic > interpolations, and Miller confused the two and left the bug there. > Miller's is a true implementation of the former -- his is a Lagrange interpolator which goes through all points -- it's algebraically identical to the cubic interpolator in csound, and so it should have a similar "sound" as any of the table-reading opcodes in csound that also employ cubic interpolation. The latter is an Hermite interpolator which uses the outside points to approximate the first derivative -- the resulting curve only passes through the middle two points, but doesn't go through the outside two; this ensures that as it's pieced together the first derivative will be continuous at the junctions. It's algebraically identical to the cubic interpolator in supercollider. They're two different approaches -- each has its own frequency response, but both are true cubics. If you want to match all four points AND the first derivatives, you have to use a 5th-order polynomial. The formulas are easily derivable using the Gaussian method, and it's easy to implement all these as a library of functions that can be accessed by the relevant objects, where the user can choose which type of interpolation he/she wants to use. Matt

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Audiomulch equivalent
by Jerome Covington 30 Mar '10

30 Mar '10

Has anybody had success building the equivalent of Audiomulch? I'm specifically interested in the looping gadget and being able to time stretch multiple loops (with pitch shifting). -- Regards, Jerome Covington . . . . : . . . . : "define audio development"

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Birds use stars - diatonic
by Mathieu Bouchard 29 Mar '10

29 Mar '10

> You can also take your values mod 12 and use those numbers to read > indices in a 12-member table you've populated with a mapping onto your > favorite scale. If your values are floats you might round them first. > You can also keep track of the whole-number quotient of your value > divided by 12 so that you can get your specific octave back as well -- > this gives you the equivalent of an "octave-pitch-class" notation, > like the kind you might find in csound. your method does not take into account that the mapping to the closest note has two different widths, 2 halftones for notes not next to a semitone interval, 1.5 halftone for those that are (Mi,Fa,Si,Do). what I was alluding to, for multiple octaves, is to use something like [wrap], so that you can use a chain of [moses] made for one octave, removing the octave number before going into [moses] and putting back right after. but since all ranges are multiples of a quartertone, one could multiply the midi note by 2, round, then go through a [tabread]. if you don't convert to quartertones, the rounding to the closest integer will conflict with the goal of rounding to the closest note, so you won't be able to get the closest note. _ _ __ ___ _____ ________ _____________ _____________________ ... | Mathieu Bouchard, Montréal, Québec. téléphone: +1.514.383.3801

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My first two works in Pd
by Pedro Oliveira 29 Mar '10

29 Mar '10

Leute, I've been struggling with Pd for a couple of months and finally I managed to kind of finish two main Projects I took along last Semester in my Masters. Of course there could be a lot of improvement but nevertheless, I'm proud of myself :) The first one is "The Sound of Nowhere", a self-sustainable sonic installation with a pretty simple and straight-forward idea: feedback. http://www.vimeo.com/10468199 And the second is "Contrapunctual Improvisation of Whatever", an Installation that works with voice input to create small phrases for improvisation. A little more complex than the previous, but rather funny. http://www.vimeo.com/10481084 I'm still organizing the source code and writing all acknowledgements before putting it online, and again, I know this may be silly and simple for most of you, but anyway, I'm excited with what I was able to do with Pd in six months or so. I hope you enjoy them :) -- Pedro Oliveira www.partidoalto.net soundcloud.com/iburiedpaul

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PIEZO ARDUINO
by Jose Luis Santorcuato 29 Mar '10

29 Mar '10

Dear list i make a project using pduino and electric piezo (analog in) all works fine, but the piezo trigger sometines repeat bangs, how i can select one bang and block the other? i stay using a edge object, but the problem persist. Best regards José -- http://www.chilemigra.cl http://arselectronicachile.blogspot.com http://www.myspace.com/santorcuato

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Pitchshifter : fft-based?
by Pierre Massat 29 Mar '10

29 Mar '10

Hi all! I was wondering if it'd possible to make a fft-base pitchshifter. I m not talking about the frequency shifter one can find in the audio examples of Pd, which doesn't eally do the same thing. Would it make any difference compared to the delay-base one, in terms of delay length in particular? Cheers! Pierre

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Pd-list March 2010