And of course I mean "cross-correlation coefficient" On Sun, Aug 8, 2021 at 3:22 PM Julius Smith <julius.sm...@gmail.com> wrote:
> 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 > -- "Anybody who knows all about nothing knows everything" -- Leonard Susskind
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