0

I have this signal:

enter image description here

It represents the rotational movement of a system. I need to define this movement, more specifically I need to find the (main) frequency of it and the amplitude of it. I believe that the long term movement could be a drift. I mostly care about the high-frequency movement.

FFT is giving this: enter image description here

Any idea? Thanks!

Alexandros Mel
  • 55
  • 6
  • 1
    You could first do a `detrend` of your signal, but you already see a peak at around 10Hz, which seems about right looking your time domain signal – rinkert Oct 08 '20 at 08:56
  • Regarding visualization: I would use a dB representation of the FFT result. – Irreducible Oct 08 '20 at 09:02
  • FFT also gives wrong amplitude (always smaller than the correct). – Alexandros Mel Oct 08 '20 at 09:12
  • It seems highly unlikely that matlab's FFT is not implemented correctly, so it's more likely that there's a misunderstanding of what it is doing. One issue I've seen many times: if you're trying to get the amplitude at some frequency, you need to divide the fft output by the fft length. There's also potentially a factor of 2, depending on whether you want the amplitude of a real-valued signal or the amplitude of a complex exponential at a particular frequency. – Eric Backus Nov 27 '20 at 03:37

0 Answers0