find the delay between two signals

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Yunyu Hu
Yunyu Hu 2022-5-13
评论： Yunyu Hu 2022-5-16
I have two signals like following:
They are the same length (200),
But d = finddelay(x,y) shows
d=0;
It cannot find the correct delay between them. Which function can be used here to get the right solution?

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Jonas
Jonas 2022-5-13
use xcorr(sig1,sig2), and use the max value of xcorr. the corresponding delay can be found at the corresponding value in the lag output (second output)
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Jonas
Jonas 2022-5-16
编辑：Jonas 2022-5-16
Ran in:
you are using the output not correctly. lag contains the corresponding lag value of the correlation calues of the first input. you need to find the lag value of the maximum correlation
dt=0.8;
x=[10,11,12,13,14,15,16,15,14,12];
t1=0:dt:(numel(x)-1)*dt;
y=[10,10,10,10,11,12,13,14,15,16,15,14,12];
t2=0:dt:(numel(y)-1)*dt;
figure;
original=subplot(3,1,1);
plot(t1,x); hold on; plot(t2,y);
title('original')
xlabel('time');
[corrVal,lag]=xcorr(x,y);
lagplot=subplot(3,1,2);
plot(lag*dt,corrVal,'-+');
xlabel('lag');
ylabel('xcorr value');
[~,maxCorrIdx]=max(corrVal);
lagAtMaxVal=lag(maxCorrIdx);
aligned=subplot(3,1,3);
plot(t1,x,'-*'); hold on; plot(t2+lagAtMaxVal*dt,y,'-s');
title('aligned');
xlabel('time')
linkaxes([original lagplot aligned],'x');
Yunyu Hu
Yunyu Hu 2022-5-16
Hi, Thanks a lot for the explaination! It is quite reasonable.
And I found the reason, why both xcorr and finddelay cannot give me the correct answer for my original signals. Because the peak is downwards.
If I change the the x and y like this:
x=20-[10,11,12,13,14,15,16,15,14,12];
y=20-[10,10,10,10,11,12,13,14,15,16,15,14,12];
and run your codes, it can also not find the correct answer.
I think this is the limitation of cross correlation. But I can do conversion on signals. :-)

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