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Fast Fourier Transform Amplitude Units

  1. Dec 3, 2009 #1
    Hi there,

    So I have a multi year time series of of heights in meters that I am working on. If I compute the FFT on the data and then calculate the amplitude as: abs(FFT)/N where N is the number of samples what units do I end up with for the amplitude? Is it still in meters?
  2. jcsd
  3. Dec 3, 2009 #2


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    Science Advisor
    Gold Member

    Yes, it is still in meters. The FFT is just taking the original data, multiplying it by exponentials (which are unitless), and summing. Dividing by N does not change the units - indeed, for the zero-frequency bin you are just averaging the original data, so it has the same units.

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