MATLAB: Xcorr

xcorr

   Could you please tell me how to understand the delay from the output of the numbers in the below program being displayed? I know the concept of xcorr. I am new to matlab, please help me get through this.

fs=100 t = 0:1/fs:1; x = sin(2*pi*t); y = sin(2*pi*t+pi/10); plot(t,x,t,y) [c, lags] = xcorr(x,y)

Thanks in advance

Best Answer

The frequency of your inputs is 1 Hz, or 2*pi radians per second

The phase lag is pi/10 radians, which corresponds to

pi/10*(1/(2*pi)) seconds. That is 5 sample points at your sampling frequency.

Look at c for c(101:110) which corresponds to lags 0 to 10. See that the maximum value occurs at lag 5, which corresonds to 0.05 seconds as expected.

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MATLAB: Time delay between two signals from the same source

You can use xcorr to determine the delay in samples and then use sampling frequency to find out the exact delay in time.

fs = 100;
t = 0:1/fs:1;
x = sin(2*pi*t);
y = sin(2*pi*t+pi/10);
[c, lags] = xcorr(x,y)

If you examine c, the maximum is at index 106, which corresponds t a lag of (see lags) 5. This means the two signals match at a delay of 5 samples. You can translate that to time by dividing the number of samples with the sampling frequency. You can also use findpeaks to automate the peak search.

HTH

MATLAB: Is the unit of Cxy from cpsd in decibel

Hi, no, the output is the cross spectrum, it is complex-valued. If you want the output in db. Use

10*log10(abs(Pxy));

For example:

   Fs = 1000;  
   t = 0:1/Fs:.296;
   x = cos(2*pi*t*200)+randn(size(t)); 
   y = cos(2*pi*t*100)+randn(size(t));  
   [Pxy,F] = cpsd(x,y,[],[],[],Fs);  
   plot(F,10*log10(abs(Pxy))); grid on;
   % compare to 
   figure;
   cpsd(x,y,[],[],[],Fs);

Best Answer

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MATLAB: Time delay between two signals from the same source

MATLAB: Is the unit of Cxy from cpsd in decibel

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