# xcorr lag input to time?

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Carly 2023년 5월 23일
편집: Carly 2023년 5월 24일
Hello,
I am trying to find the cross-correlation of two 1x180000 vectors (sigX and sigY). The sampling frequency is fs=1000. I am trying to find the xcorr with a lag of 30 s. How do I input the lag of -30:30 sec to the xcorr function given the sampling rate?
[c,lags] = xcorr(x,y,LAGS,'normalized');
The input 'm asking about is LAGS. Is this input in samples or time? If time, what unit of time?
Thank you

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### 채택된 답변

David Goodmanson 2023년 5월 24일
편집: David Goodmanson 2023년 5월 24일
Hi Carly,
lags is a dimensionless index, so it's in samples (it has to be samples since xcorr has no way of knowing what fs might be). Since sampling frequency times a time interval is the number of samples, the input to xcorr is LAGS = (-30:30)*fs, a dimensionless index.
(This is assuming that 30* fs is exactly an integer, otherwise some rounding will be involved).
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Carly 2023년 5월 24일
thank you!

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