In signal processing, a periodogram is an estimate of the spectral density of a signal. The term was coined by Arthur Schuster in 1898.]]
When a periodogram is used to examine the detailed characteristics of an FIR filter or window function, the parameter is chosen to be several multiples of the non-zero duration of the sequence, which is called zero-padding (see ). When it is used to implement a filter bank, is several sub-multiples of the non-zero duration of the sequence (see ).
One of the periodogram's deficiencies is that the variance at a given frequency does not decrease as the number of samples used in the computation increases. It does not provide the averaging needed to analyze noiselike signals or even sinusoids at low signal-to-noise ratios. Window functions and filter impulse responses are noiseless, but many other signals require more sophisticated methods of spectral estimation. Two of the alternatives use periodograms as part of the process:
- The method of averaged periodograms,