Windowing premultiplies input data supplied to the FFT with a value that smoothly decreases to zero at each end of data.
The purpose is to reduce "leakage" aberrations in the FFT output that are introduced by sudden changes in the data at the start and end of data. Much research has been applied to the selection of the proper "windowing function", so Igor´s FFT supplies many of them:
- Blackman361, Blackman367, Blackman492, Blackman474
- Cos1, Cos2, Cos3, Cos4
- KaiserBessel20, KaiserBessel25, KaiserBessel30
- Poisson2, Poisson3, Poisson4
Here is a demonstration of how windowing can improve the Fourier Transform result:
Igor provides a standalone Hanning command to window data without involving the FFT. The
#include <DSP Window Functions>
statement loads the Parzen, Welch, Kaiser, Hamming, BlackmanHarris3, and KaiserBessel functions which also window data without involving the FFT.
- Harris, F.J., "On the use of windows for harmonic analysis with the discrete Fourier Transform", Proc, IEEE, 66, 51-83, 1978.