How to know which Signal is delayed !

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Susan
Susan on 22 Aug 2011
Dear all, I have my code below for real data samples. I already tested the xcorr delay calculation method with different data and it produced the right answer but with the real data, I am not sure how to know after calculating the delay which of the two signal is the delayed version of the other?
x = sample1(:,1);
X = (x).';
y = sample2(:,1);
Y = (y).';
figure;
clf
subplot(3,1,1);
[xi,f]=ksdensity(X);
plot(f,xi);
line(repmat(X,2,1),repmat([0;0.1*max(xi)],1,length(X)),'color','r' );
subplot(3,1,2);
[xi,f]=ksdensity(Y);
plot(f,xi);
line(repmat(Y,2,1),repmat([0;0.1*max(xi)],1,length(Y)),'color','r' );
[Rxx,lags] = xcorr(X,Y);
[Z,delay] = max(Rxx);
lags(delay);

Answers (1)

Fangjun Jiang
Fangjun Jiang on 22 Aug 2011
Susan, Others don't have your data sample1 and sample2 so won't be able to look at your data. Would the sign of lags(delay), be positive or negative, tell you whether Y is the delay of X, or X is the delay of Y?
y is 10 steps lag behind x, when running
[Rxx, lags] = xcorr(x, y);
[Y, I] = max(Rxx);
lags(I)
It returns -10, meaning y is 10 steps lag behind x
If you run
[Rxx, lags] = xcorr(y, x);%switch order of x and y
[Y, I] = max(Rxx);
lags(I)
It returns 10, meaning x is 10 steps ahead of y
  4 Comments
Fangjun Jiang
Fangjun Jiang on 23 Aug 2011
You could visually inspect your data to get a sense whether the result is in the ballpark.
Susan
Susan on 23 Aug 2011
It would not be accurate but the fact that swapping both x,y gives different results I think its a sign the delay calculated is not right.. Any idea where I am going wrong?

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