Hi Klaus, I am late to this (just read some of the thread with interest), and I have a question: what do you mean by "1 > corr(t,l,r) > 0" ? It appears to be "parsed" left to right, so that the 2nd ">" only sees "1>0" most (all?) of the time, which is always true (1) of course (so no "else" activated). Maybe you want something like "abs(corr(t,l,r)) > 0.95" ? (i.e., 95% correlation deemed to be "panned mono"). I'm taking the absolute value because I assume you don't care if the left channel is merely the negative of the right (unless that's an accepted cheezy "stereoizer" of sorts).
FYI, this is what we call a time-domain "normalized cross-correlation" or "correlation coefficient" measurement (official buzzwords) Cheers, Julius On Sun, Aug 8, 2021 at 10:07 AM Klaus Scheuermann <kla...@posteo.de> wrote: > Dear Dario, > > cool, your corr function gives me the desired results. At least when > feeding it to a meter. > > Here is my test audio which contains vocals in mono-mid, mono-left, > mono-right, mono-half-left, mono-half-right, stereo: > https://cloud.4ohm.de/s/y9oZzqFGyrZT5ej > For mono-mid, mono-half-left, mono-half-right it shows 1. > For mono-left, mono-right it shows 0. > For stereo it shows values between 0 and 1. > > I would like to detect mono signals that are not exactly in the middle and > put them there. Stereo signals should be unchanged. > > My code is here, but for some reason it does not work correctly. > Especially when corr shows 0, ba.if does not go to the else-path. > > import("stdfaust.lib"); > avg(t, x) = fi.pole(p, (1 - p) * x) // 1-pole lowpass as average > with { > p = exp((((-2.0 * ma.PI) / t) / ma.SR)); > }; > var(t, x) = avg(t, (x - avg(t, x)) ^ 2); // variance > sd(t, x) = sqrt(var(t, x)); // standard deviation > cov(t, x1, x2) = avg(t, (x1 - avg(t, x1)) * (x2 - avg(t, x2))); // > covariance > corr(t, x1, x2) = cov(t, x1, x2) / (sd(t, x1) * sd(t, x2)) : _ ; // > correlation > t = 0.5; // averaging period in seconds > correlate_meter(x,y) = x,y <: x , attach(y, (corr(t) : hbargraph("corr",-1 > ,1))) : _,_; > correlate_correct(t,l,r) = ba.if(1 > corr(t,l,r) > 0 , l, (l+r)) , ba.if(1 > > corr(t,l,r) > 0 , r, (l+r)); > process = _,_ : correlate_meter : correlate_correct(t); > > Am I doing the ba.if wrong? > > Thank s very much, > Klaus > > > On 04.08.21 18:25, Dario Sanfilippo wrote: > > I had implemented a few statistics function a while back, kindly taken > from Wikipedia, and they seem to produce the expected values mentioned on > the webpage. I hope that these can be useful. > > Ciao, > Dr Dario Sanfilippo > http://dariosanfilippo.com > > import("stdfaust.lib"); > avg(t, x) = fi.pole(p, (1 - p) * x) // 1-pole lowpass as average > with { > p = exp((((-2.0 * ma.PI) / t) / ma.SR)); > }; > var(t, x) = avg(t, (x - avg(t, x)) ^ 2); // variance > sd(t, x) = sqrt(var(t, x)); // standard deviation > cov(t, x1, x2) = avg(t, (x1 - avg(t, x1)) * (x2 - avg(t, x2))); // > covariance > corr(t, x1, x2) = cov(t, x1, x2) / (sd(t, x1) * sd(t, x2)); // correlation > ph0 = os.phasor(2.0 * ma.PI, 200); > red = sin(ph0) + .35 * sin(ph0 * 3.0) + .91 * sin(ph0 * 5.0); > blue = sin(ph0) + .5 * sin(ph0 * 3.0) - .5 * sin(ph0 * 5.0); > red1 = sin(ph0) + sin(ph0 * 3.0); > blue1 = sin(ph0) - sin(ph0 * 3.0) / 3.0; > t = 1.0; // averaging period in seconds > process = (red , blue : corr(t)) , (red1 , blue1 : corr(t)); > > > > On Wed, 4 Aug 2021 at 16:52, Klaus Scheuermann <kla...@posteo.de> wrote: > >> Thanks Giuseppe, >> >> I checked it out, but somehow it still does not give me the desired >> result... >> I did some more research and found this, which indicates that it can be >> done with arctan more easily. >> >> The way this is done on phase (correlation) meters in audio equipment is >> rather simple: >> >> Phase = arctan(L/R) >> >> With phase of 45 or 225 = 1, and phase of 135 and 315 (-45) is -1. >> >> Essentially, the Y Axis is the L, and the X axis is the R. The phase is >> simply the polar angle of the vector between the two. >> >> This type of meters will show 1 if the signal is mono, and -1 if the left >> and right are perfectly phase inverted. >> >> Notice however, that phase meters of this type also account for the >> magnitude in the polar coordinates. So: >> >> Magnitude = (L^2 + R^2)^1/2 >> >> Thus the actual meter display is a normalised version of: >> >> Correlation = Phase * Magnitude >> >> I'm not sure that satisfies your requirements, but this answers the >> question in the subject. >> >> So I transfered this to faust, but it still behaves weired... >> import("stdfaust.lib"); >> phase(l,r) = (l/r) : aa.arctan; >> magnitude(l,r) = (l^2 + r^2)^1/2; >> correlate(l,r) = phase(l,r) * magnitude(l,r); >> correlate_meter(x,y) = x,y <: x , attach(y, (correlate : hbargraph("corr" >> ,-1,1))) : _,_; >> process = _,_ : correlate_meter: _,_; >> >> Any ideas? >> >> Klaus >> >> On 03.08.21 14:48, Giuseppe Silvi wrote: >> >> Hi Klaus, >> The filters are necessary to obtain a -1 +1 range, I think. >> >> import("stdfaust.lib"); >> >> correlate(l,r) = l*l ,r*r , l*r : par(i,3, si.smooth(0.9)) : sqrt, sqrt, _ : >> *,_ : /; >> correlate_meter(x,y) = x,y <: x , attach(y, (correlate : >> hbargraph("corr”,-1,1))); >> >> process = correlate_meter; >> >> Try playing with the si.smooth coefficient. >> >> best, >> giuseppe >> >> >> On 3 Aug 2021, at 14:09, Klaus Scheuermann <kla...@posteo.de> >> <kla...@posteo.de> wrote: >> >> Could it be something like this? >> >> (according to the 'correct' algorithm in >> https://www.beis.de/Elektronik/Correlation/CorrelationCorrectAndWrong.html ) >> import("stdfaust.lib"); >> >> correlate(l,r) = l*l ,r*r , l*r : sqrt, sqrt, _ : *,_ : / :_; >> correlate_meter(x,y) = x,y <: x , attach(y, (correlate : >> hbargraph("corr",-1,1))) : _,_; >> >> process = _,_ : correlate_meter: _,_; >> >> I am not sure about the lowpass filters though. Maybe not needed in the >> digital domain? >> >> Also, my code only returns -1 or 1 while it should be returning a range of >> -1 and 1, right? >> >> The correlation is either expressed in % from -100% to +100% or as the >> correlation factor, which ranges from -1 to +1. Note that due to the >> correlation algorithm the level of both signals does not matter, i.e., it >> does not influence the measured result. >> >> When a mono source is used for a stereo signal both stereo channels will be >> +100% correlated. When e.g. in a stereo signal both channels contain >> completely different signals, e.g. left (and only left) is the trumpet and >> right (and only right) is the guitar these stereo channels will be 0% >> correlated. With a third instrument appearing in both channels, the >> correlation will be somewhere between 0 and +100%. >> >> >> Ideas? >> Danke :) >> Klaus >> >> >> >> >> On 03.08.21 12:48, Klaus Scheuermann wrote: >> >> Hello List, >> >> I just wondered, if anyone has implemented a stereo audio correlation >> meter/analyser in faust? >> >> If yes - great! >> If no - I have another project :) >> >> Here is what I found about the algorithm(s): >> https://www.beis.de/Elektronik/Correlation/CorrelationCorrectAndWrong.html >> >> >> I never learned analog electronic schematics, but it seems it should not >> be extremely hard to transfer to faust. >> >> Cheers, Klaus >> >> >> >> _______________________________________________ >> Faudiostream-users mailing list >> Faudiostream-users@lists.sourceforge.nethttps://lists.sourceforge.net/lists/listinfo/faudiostream-users >> >> _______________________________________________ >> Faudiostream-users mailing >> listFaudiostream-users@lists.sourceforge.nethttps://lists.sourceforge.net/lists/listinfo/faudiostream-users >> >> _______________________________________________ >> Faudiostream-users mailing list >> Faudiostream-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/faudiostream-users >> > _______________________________________________ > Faudiostream-users mailing list > Faudiostream-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/faudiostream-users > -- "Anybody who knows all about nothing knows everything" -- Leonard Susskind
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