ABSTRACT
A sine-wave signal will have only a single-frequency component in its spectrum, that is, the frequency of the tone. Since only a pure sine wave can have a single component in its frequency spectrum, the output must have other frequencies in its spectral composition. In the case of harmonic distortion, the frequency spectrum of the distorted signal will consist of the fundamental (which is the same frequency as the input sine wave) plus harmonic frequency components that are at integer multiples of the fundamental frequency. If the system has good linearity (which implies low distortion), then the total harmonic distortion (THD) will be a smaller number than that for a system having poorer linearity (higher distortion). It is desirable to visualize how the various harmonics increase or decrease as the amplitude of the input sine wave is changed. The THD is a figure of merit for the quality of the transmission of a signal through a system having some nonlinearity.
