Control spectral leakage in frequency analysis
When analyzing a finite segment of a signal, the FFT assumes the segment repeats infinitely. If the signal doesn't complete exact cycles within the window, discontinuities cause spectral leakage - energy spreads to adjacent frequency bins.
Rectangular: Best frequency resolution, worst leakage (-13 dB sidelobes)
Hann: Good general-purpose window, -31 dB sidelobes
Hamming: Optimized for minimum near-sidelobe level, -42 dB
Blackman: Excellent sidelobe suppression (-58 dB), wider main lobe
Kaiser: Adjustable tradeoff via β parameter