What is the significance of the first zero up-crossing of a cross-correlation? The signals being correlated are cosines signals with some phase difference.
EDIT 1 : Cross-correlation plot attached. The signals are cosines with phase difference and may be with some low frequency components.
Sampling frequency of the measured signal is taken as 50Hz
Cross correlation obtained using:
Cxx=fftshift(ifft(fft(x,N).*conj(fft(y,N))))/(norm(x) * norm(y));