Types of Windows for Spectral Leakage Treatment

Applying a window to--or windowing--a signal in the time domain requires multiplying the signal by the window function. Because multiplication in the time domain is equivalent to convolution in the frequency domain, the spectrum of the windowed signal is a convolution of the spectrum of the original signal with the spectrum of the window. Thus, windowing changes the shape of the signal in the time domain, as well as affecting the spectrum that you see.

What type of window should you use? The answer depends on the type of signal you have and what you are looking for. Choosing the correct window requires some prior knowledge of the signal that you are analyzing. The following table shows the different types of windows and the signal types they are appropriate for.

Window	Signal Type and Description	Applications
Rectangular (no window)	Transient signals that are shorter than the length of the window; truncates a window to within a finite time interval.	Order tracking, system analysis (frequency response measurements) with pseudorandom excitation, separation of two tones with frequencies very close to each other, but with almost equal amplitudes
Hanning	Transient signals that are longer than the length of the window	General-purpose applications, system analysis (frequency response measurements) with random excitation
Hamming	Transient signals that are longer than the length of the window; a modified version of the Hanning window that is discontinuous at the edges	Often used in speech signal processing
Triangle	Window that is the shape of a triangle	No special applications
Blackman	Transient signals; similar to Hanning and Hamming windows but adds one additional cosine term to reduce ripple
Flat Top	Has the best amplitude accuracy of all the windows but comes at the expense of frequency selectivity	Accurate single tone amplitude measurements when there are no nearby frequency components

Note In many cases, you might not have sufficient prior knowledge of the signal, so you need to experiment with different windows to find the best one.

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