Spectral density

Relative importance of certain frequencies in a composite signal

In signal processing, the power spectrum S x x ( f) {\displaystyle S_{xx}(f)} of a continuous time signal x ( t) {\displaystyle x(t)} describes the distribution of power into frequency components f {\displaystyle f} composing that signal. Fourier analysis shows that any physical signal can be decomposed into a distribution of frequencies over a continuous range, where some of the power may be concentrated at discrete frequencies. The statistical average of the energy or power of any type of signal (including noise) as analyzed in terms of its frequency content, is called its spectral density.

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