How to find repetitive patterns using autocorrelation

My aim is to find repetitive patterns in an audio clip. I need to find one 'bar' of audio and I think autocorrelation should do justice. But just how do I go about this? I'm not sure what to do after using the xcorr function. For eg, in a simple case where the values could be x=[1 2 3 1 2 3 1 2 3], and ac=xcorr(x); what do I do next to extract just [1 2 3]?

Answer 1

[Jason Kaeding]

Wouldn't you see spikes in your xcorr result corresponding to the period of the signal? If you can find the spacing (N) between two spikes, then you would just extract x(1:N) where N is your period length. You might need to shift (1:N) depending on the location of your reference spike.

You would have to define some rules/math to determine where the "spikes" are.