Frequency domain is a term used to describe the analysis of mathematical functions or signals or periodic movement with respect to frequency.
A graph of the time domain shows the evolution of a signal in time, while a frequency graph shows the components of the signal according to the frequency in which they oscillate within a certain range. A frequency representation also includes the information about the phase shift that must be applied to each frequency in order to recombine the frequency components and be able to recover the original signal again.
The domain of the frequency is related to the Fourier series, which allow to decompose a periodic signal into a finite or infinite number of frequencies.
The domain of the frequency, in the case of non-periodic signals, is directly related to the Fourier Transform.
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