[PD] Phase and impulse response measurement

Martin Schied crinimal at gmx.net
Fri Nov 5 03:10:39 CET 2010


  On 04.11.2010 16:14, Mathieu Bouchard wrote:
> On Thu, 4 Nov 2010, Martin Schied wrote:
>
>>       Hi everyone,
>>       i wondered if someone made a patch measuring the PHASE of a 
>> reference signal compared to measured signal
>>
>> you could one of the cross-correlation externals to measure the time 
>> delay between 2 signals. (there's one external in iem_tab from 
>> pd-extended I remember and there are possibly more). If that's useful 
>> for you I created a similar, fft based patch using vanilla objects I 
>> can post here. However correlation doesn't directly measure phase 
>> differences of separate frequency bands but the delay of the signal 
>> over all frequencies.
>
> What do you mean ? If you get the imaginary part of the logarithm of 
> the cross correlation, it gives you a list of phase differences 
> corresponding to each frequency bin, right ?
if your's still in the frequency domain you can do such things, but the 
iem_tab external output is already time domain - also I'm no math guru 
so you definitely answer this better...
I took the math from 
http://www.engr.udayton.edu/faculty/jloomis/ece561/notes/xcorr/xcorr.html which 
is offline now unfortunately, but the explanation was very good. hope it 
comes back. ;)
>
> (that's equal to the atan2 between the real and imaginary parts of the 
> cross-correlation)
attached a correlation and a "phase difference" patch. it's very basic 
and may contain errors ;)

Martin




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