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Asked: 2026-05-18T21:25:01+00:00

I am trying to use Excel’s (2007) built in FFT feature, however, it requires

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I am trying to use Excel’s (2007) built in FFT feature, however, it requires that I have 2^n data points – which I do not have.

I have tried two things, both give different results:

  1. Pad the data values by zeros so that N (the number of data points) reach the closest power of 2
  2. Use a divide-and-conquer approach i.e. if I have 112 data points, then I do a FFT for 64, then 32, then 16 (112=64+32+16)

Which is the better approach? I am comfortable writing VBA macros but I am looking for an algorithm which does not require the constraint of N being power of 2. Can anyone help?

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  1. Editorial Team

    Padding with zeros is the right direction, but keep in mind that if you’re doing the transform in order to estimate frequency content, you will need a window function, and that should be applied to the short block (i.e., if you have 2000 points, apply a 2000 point Hann window, then pad to 2048 and calculate the transform).

    If you’re developing an add-in, you might consider using one of the many FFT libraries out there. I’m a big fan of KISS FFT by Marc Borgerding. It offers fast transforms for many blocksizes, essentially any blocksize that can be factored into the numbers 2,3,4, and/or 5. It doesn’t handle prime number sized blocks though. It’s written in very plain C, so should be easy to port to C#. Or, this SO question suggests some libraries that can be used in .NET.

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