# Finding Peaks in an Autocorrelation Function

I'm trying to find the period of a signal. I've used FFT to compute the autocorrelation of the signal. As can be seen from the autocorrelation function (plotted below) I obtained, there are 70 sample between peaks which actually indicates the period of my signal.

What is the best way to extract the indices of these peaks from such a data?

You can then detect peak by detecting local maxima - if $X(n) = \max_{k \in [k-W, k+W]} X(k)$, then $n$ is a peak. $W$ is a scale factor which indicates how narrow and close to each other you allow your peaks to be.