The FFT function uses a Fast Fourier Transform (FFT) algorithm to compute the discrete Fourier Transform (DFT) of each signal in one or more input table columns. A signal can be either real or complex, and can have one, two, or three dimensions. If the signal length is not a power of two, the function either pads or truncates it to the closest power of two.
This is the DFT of a time sequence of length N, 0..N-1:
X(k) = Xk(N - k)
where k ϵ 0..N-1.
Therefore:
- The FFT of a time sequence of length 1 is the one-element sequence itself.
- The FFT of a time sequence of length 2 has only real values.
- The FFT of a time sequence of length 4 or greater has conjugate symmetry.
To recover the original signals, use the IFFT (ML Engine) function.