Find period of a signal out of the FFT

Question

I have a periodic signal I would like to find the period.

Since there is border effect, I first cut out the border and keep N periods by looking at the first and la

Answer 1

The peak in an FFT magnitude result represents frequency, which is the reciprocal of the period. Multiply the frequency index reciprocal by the FFT window length to get the period result in the same units at the window length.