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I was very surprised to find an apparent limitation to a FFT on a simple signal.

Let's consider a timeseries made of L=100 points, and simply composed of the sum of two sinus waves: one with a wavelength of 7 points, the other with a wavelength of 13 points (the phase or amplitude does not matter).

If you compute the FFT of this signal, you won't find exactly the two harmonics, because L is not an exact multiple of 7 or 13.

How do you deal with this problem? Interpolation of the data on a higher resolution?

Edit : this problem can be "minimized" with zero padding

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  • $\begingroup$ Google "zero padding" $\endgroup$
    – DrManhattan
    Commented Nov 9, 2020 at 9:19
  • $\begingroup$ Thank you ! Problem solved. $\endgroup$
    – François Ritter
    Commented Nov 9, 2020 at 9:56
  • $\begingroup$ Problem solved? Problem starts! While you are "padding" do not forget to "window"! $\endgroup$
    – hyportnex
    Commented Nov 9, 2020 at 14:58

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