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 <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 > <mailto: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> >>> <mailto:kla...@posteo.de> wrote: >>> >>> Could it be something like this? >>> >>> (according to the 'correct' algorithm in >>> https://www.beis.de/Elektronik/Correlation/CorrelationCorrectAndWrong.html >>> <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 >>>> <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.net >>>> <mailto:Faudiostream-users@lists.sourceforge.net> >>>> https://lists.sourceforge.net/lists/listinfo/faudiostream-users >>>> <https://lists.sourceforge.net/lists/listinfo/faudiostream-users> >>> _______________________________________________ >>> Faudiostream-users mailing list >>> Faudiostream-users@lists.sourceforge.net >>> <mailto:Faudiostream-users@lists.sourceforge.net> >>> https://lists.sourceforge.net/lists/listinfo/faudiostream-users >>> <https://lists.sourceforge.net/lists/listinfo/faudiostream-users> > _______________________________________________ > Faudiostream-users mailing list > Faudiostream-users@lists.sourceforge.net > <mailto:Faudiostream-users@lists.sourceforge.net> > https://lists.sourceforge.net/lists/listinfo/faudiostream-users > <https://lists.sourceforge.net/lists/listinfo/faudiostream-users> >
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