Matlab: cross-correlation and autocorrelation 互相關與自相關

cross-correlation 互相關
autocorrelation 自相關

For autocorrelation function in Matlab:
autocorr - Econometrics Toolbox - for statistics. 😳
xcorr - Signal Processing Toolbox - for engineers!! 😄

To use xcorr:
xcorr(x, y) => cross-correlation of discrete signals x and y.
xcorr(x) => autocorrelation of x. Special condition of cross-correlation since auto correlation is the cross-correlation of signal x and shifted version of itself.

Autocorrelation is a special case of cross-correlation.

Autocorrelation may be used for pitch (fundamental frequency, F0) detection.

References:

Cross-correlation (Wikipedia)
Autocorrelation (Wikipedia)
Pitch detection algorithm (Wikipedia)
D. Gerhard. Pitch Extraction and Fundamental Frequency: History and Current Techniques, technical report, Dept. of Computer Science, University of Regina, 2003.