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Frequency domain

Frequency domain is a term used to describe the analysis of mathematical functions with respect to frequency.

Speaking non-technically, a time domain graph shows how a signal changes over time, whereas a frequency domain graph shows how much of the signal lies within each given infinitesimal frequency band over a range of frequencies. A spectrum analyser on a stereo is an example of a frequency domain graph.

If a signal is known in the time domain, a frequency domain graph can be constructed using a technique known as a Fourier transform. This technique relies on Fourier series.