Windows
In order to reduce the effect of leakage, it is necessary to see to it that the signal level is zero at the beginning and end of the time record. Multiplying the data samples by a so-called “windowing” or “weighting” function, which can have several different shapes, does this. The most common forms of windows and their uses are considered next.
If there is no windowing function used, this is called "Rectangular", "Flat", or "Uniform" windowing. In the figure above, the effect of the data truncation can be seen as discontinuities in the windowed waveform. The FFT analyzer only knows what is in the time window, or time record. It assumes the actual signal contains the discontinuities, and they are the cause of the leakage seen in the previous figure. Leakage could be avoided if the input waveform zero crossings were synchronized with the sampling times, but this is impossible to achieve in practice.
Windowing for Transient Signals
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