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A spectrogram displays a signal's changing local frequency spectrum, usually by color proportional to squared short-time Fourier transform magnitude. With window function $w$, one convention isThe window selects a neighborhood of time $t$ before taking its Fourier transform. A sinusoid gives a persistent frequency ridge, while a brief pulse spreads across frequencies and occupies a short time range.

A longer window separates nearby persistent frequencies more clearly but mixes events across a longer interval. A shorter window localizes transients but broadens their spectral features. Changing the window function changes this tradeoff and the spectral leakage. Zero padding can sample the displayed frequency curve more finely; it does not add observed data or restore the resolution lost through a short measurement interval. The phase is discarded in the plotted squared magnitude, so the spectrogram should not be confused with a complete set of complex transform coefficients.