# phase shift using xcorr

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ZIYI LIU 2022 年 5 月 17 日

Dear all, I have a question really need your help. I have two functions, and I want to know their phase shift based on the period, but not the lags.
Here is the code: (I just modified the code from other questions)
t = 1 :0.1: 20;
phaseshift= pi/2;
s1 = sin (2*t);
s2 = sin (2*t+ phaseshift);
figure(1); clf;
plot (t,s1,'r', t,s2,'k');
figure;
[c,lag] = xcorr(s1,s2);
plot(lag,c)
[c,lags]=xcorr(s1,s2);
[~,iLag]=max(c(find(lags==0):end))
s3=circshift(s2,[0 iLag]);
figure;
plot(t,s1,t,s3)
I know the lags, but how do I get the phase shift based on 2*pi? (eg. the phase shift betweenthese two lines is pi, 1/2 period, because 2*t)
Thank you very much!
BEST,
zIYI

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### 回答 (1 件)

VBBV 2022 年 5 月 17 日
t = 1 :0.1: 20;
phaseshift= pi/2;
s1 = sin(2*t);
s2 = sin(2*t+ phaseshift);
figure(1); clf;
plot (t,s1,'r', t,s2,'k'); figure;
[c,lag] = xcorr(s1,s2);
plot(lag,c) [c,lags]=xcorr(s1,s2);
[~,iLag]=max(c(find(lags==pi):end)) % compare with pi
iLag = 1×0 empty double row vector
s3=circshift(s2,[0 iLag]);
figure;
plot(t,s1,t,s3) ##### 1 件のコメント表示非表示 なし
ZIYI LIU 2022 年 5 月 17 日
Hi VBBV,
Yes, I got the lags of the max c is around 8, but how do I connect the x with phase shift?
For example, we don't know the phase shift, we only have two data like the lines, and want to know the phase shift between these two lines. Now, we have the lags is 8, how do we know the phase shift is pi/2(or 1/4 period)?
Thanks!

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