> whether a [cpole~] filter like [vcf~] could be obtained with [biquad~].
I meant at least the real output of [vcf~] 2014-07-24 14:28 GMT-03:00 Alexandre Torres Porres <por...@gmail.com>: > yep, totally makes perfect sense to me now that it is a [cpole~]. > > I guess you can consider (ampcorrect * oneminusr) as a gain factor and > multiply the input signal by this much before getting it to a [cpole~] with > the same coefficients, and voilá... although getting all these > coefficients to come up in a vanilla patch seems a lot of trouble... > > But what I'm really and still dying to learn/figure out is whether a > [cpole~] filter like [vcf~] could be obtained with [biquad~]. My intuition > said: Yes. But after a few experiments I'm changing my mind... Can anyone > just confirm me that? > > What drove my intuition is the attached patch, which is a biquad~ filter > made of raw filters I derived from mmb's work. If it made any sense is > because it is implemented with [cpole~] and [czero~] objects, so it seemed > that a set of biquad coefficients could result in just a couple of > coefficients for one [cpole~]. But then, by checking it out and trying to > do it, it doens't seem possible to get a coordinate pair for a [cpole~] > with biquad coefficients... hmmm, bummer. > > Any thoughts? > > thanks > > > 2014-07-24 13:33 GMT-03:00 Miller Puckette <m...@ucsd.edu>: > > Yep, vcf~ isn't a 2-pole real filter but a 1-pole complex one (although >> its second outlet -- I think -- should be similar to a 2-pole real >> filter's output in theory, but in reality should be numerically more >> precise.) >> >> I'll change the comment to something vaguer and more descriptive in the >> code.. >> >> Unless I'm badly mistaken, vcf~ is simply a cpole~ with extra stuff to >> compute >> the coefficient built in. There's no 'x2' because the input is taken to >> be >> real-valued. >> >> cheers >> M >> >> On Thu, Jul 24, 2014 at 01:18:28PM -0300, Alexandre Torres Porres wrote: >> > >> The real part may be used as a resonant >> > >> bandpass filter and the imaginary as a >> > >> resonant low-pass filter, but they can be >> > >> combined to make other possibilities." >> > >> > > what sort of possibilities??? >> > >> > I wouldn't expect much about this. I guess it's like any other filters >> that >> > can be combined in many ways. >> > >> > Another thing I wanted to inquire is about bp~ having a frequency >> response >> > that is not symmetric. The lower part of the spectrum has more energy. >> > Could one consider it more of a "resonant low-pass filter", similar to >> > [vcf~]'s second outlet? >> > >> > By the way, while we're at it, I'd like to share something that may not >> be >> > too important, but it's related. I was able to implement [cpole~] in >> > [fexpr~]. Here it goes: >> > >> > expr 1: >> > >> > [fexpr~ $x1 + ($x3 * $y1) - ($x4 * $y2); >> > $x2 + ($x4 * $y1) + ($x3 * $y2)] >> > >> > if we consider $x3 and $x4 as variables named, respectively, coefr >> > (coeficient for the real part) and coefi (coeficient for the imaginary >> > part), we then have: >> > >> > expr 2: >> > >> > *[fexpr~ $x1 + (coefr * $y1) - (coefi * $y2);* >> > *$x2** + (*coefi * $y1) + (coefr * $y2)] >> > >> > Now, by checking the code of [vcf~] I was able to narrow down to its >> core >> > formula, which is something like this >> > >> > expr 3: >> > >> > *ampcorrect * oneminusr* * *f1 + (coefr * re2) - (coefi * im)*; >> > *(coefi * re2) + (coefr * im)* >> > >> > the bolded letters in "expr 3" seem to match perfectly to "expr 2". The >> > differences are underlined ($x2 in expr 2 and ampcorrect/oneminusr in >> expr >> > 3). >> > >> > That gets me closer to being able to implement [vcf~] with a [cpole~] I >> > guess, but I find it weird that the imaginary output does not have the >> $x2 >> > signal input to be added to the rest of the expression. I worry that >> > actually prevents it from being successfully implemented with [cpole~]. >> Am >> > I missing something? >> > >> > Anyway, the thing is that I'm still really curious to learn wether vcf~ >> is >> > a "two pole" filter or a "one complex pole" filter, and the reason >> behind >> > it is because I believe we could make a biquad~ version of [vcf~] (at >> least >> > for its real output). That's the bottom line. >> > >> > cheers >> > >> > >> > >> > >> > 2014-07-24 6:45 GMT-03:00 i go bananas <hard....@gmail.com>: >> > >> > > just chipping in with my 2 cents that it would be fantastic to get >> more >> > > documented info on all this. >> > > >> > > especially curious about: "but they can be combined to make other >> > > possibilities." >> > > >> > > what sort of possibilities??? >> > > >> > > >> > > On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres < >> por...@gmail.com >> > > > wrote: >> > > >> > >> Hi Miller, still trying to get my head around this. But anyway, one >> thing >> > >> I have to note is that the source code of [vcf~] says it is a "two >> pole >> > >> filter", not a "one complex pole" filter. >> > >> >> > >> Should that description be changed? If not, why? >> > >> >> > >> thanks >> > >> >> > >> >> > >> 2014-04-12 14:13 GMT-03:00 Miller Puckette <m...@ucsd.edu>: >> > >> >> > >> Yep - vcf~ is essentially a wrapper for cpole~. >> > >>> >> > >>> cheers >> > >>> M >> > >>> >> > >>> On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres >> wrote: >> > >>> > that's great to know, thanks! >> > >>> > >> > >>> > Let me just see if I get a bit of the theory. Can I get [vcf~] >> with >> > >>> just >> > >>> > one [cpole~] object and the right coeficients? >> > >>> > >> > >>> > Cheers >> > >>> > >> > >>> > >> > >>> > 2014-04-12 13:36 GMT-03:00 Miller Puckette <m...@ucsd.edu>: >> > >>> > >> > >>> > > They're quite different. bp~ is the cheapest possible bandpass >> > >>> filter >> > >>> > > (as far as I know). vcf~ is a one-pole complex filter whose >> outputs >> > >>> are >> > >>> > > the real and imaginry parts. The real part may be used as a >> resonant >> > >>> > > bandpass filter and the imaginary as a resonant low-pass >> filter, but >> > >>> > > they can be combined to make other possibilities. >> > >>> > > >> > >>> > > It's possible to graph their frequency responses using the help >> patch >> > >>> > > "H10.measurement.pd' in 3.audio.examples. >> > >>> > > >> > >>> > > cheers >> > >>> > > Miller >> > >>> > > >> > >>> > > On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres >> Porres >> > >>> wrote: >> > >>> > > > Hi there, who can confirm that both [bp~] and [vcf~] are >> exactly >> > >>> the >> > >>> > > really >> > >>> > > > same thingy? The code looks quite different... >> > >>> > > > >> > >>> > > > Moreover, why the two outlets for vcf~? Help doesn't say >> anything. >> > >>> > > > >> > >>> > > > Thanks >> > >>> > > >> > >>> > > > _______________________________________________ >> > >>> > > > pd-l...@iem.at mailing list >> > >>> > > > UNSUBSCRIBE and account-management -> >> > >>> > > http://lists.puredata.info/listinfo/pd-list >> > >>> > > >> > >>> > > >> > >>> >> > >> >> > >> >> > >> _______________________________________________ >> > >> Pd-list@lists.iem.at mailing list >> > >> >> > >> UNSUBSCRIBE and account-management -> >> > >> http://lists.puredata.info/listinfo/pd-list >> > >> >> > >> >> > > >> > >
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