xcorr lag input to time?

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

Answer 1

[David Goodmanson]

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).

[Carly]

thank you!