MATLAB: Cross-correlation of two signal always shows unexpected 0 lag

Question

Hi,everyone, I got a very strange issue.

b is a signal of 251 samples. c is got by shifting b by 5 sample. (b and c are attached).

But when I do xcorr on b and c, the max correlation always occurs at 0 lag. which I do not understand. Can someone help?

Below is my code. Thank you.

load b.mat
load c.mat
figure;
plot(b);hold on;
plot(c);
[r,lag] = xcorr(b,c,'coeff');
[m, i_max]=max(r);
shift=lag(i_max);
% plot(lag,r);
display(shift);

Answer 1

You may want to try

[r,lag] = xcorr(b-mean(b),c-mean(c),'coeff');

HTH