Hi Klaus,
I suppose the fixed magnitude line is
magnitude(l,r) = (l^2 + r^2)^(1/2);
and you can use `atan` in phase().
import("stdfaust.lib");
//phase(l,r) = (l/r) : aa.arctan;
phase(l,r) = (l/r) : atan;
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 = os.osc(10),os.osc(10.1) <: _,_,phase, magnitude, correlate;//,
correlate_meter;
> On 4 Aug 2021, at 16:50, Klaus Scheuermann <[email protected]> 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 <[email protected]>
>>> 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
>>>>
>>>>
>>>>
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>>>>
>>>>
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