On the other hand, when it comes to recording voice or music and reproducing it as close to the original as possible, then distortion is always undesirable. Classification and measurement of these unwanted distortions is discussed below.
Harmonic vs. no harmonic distortion
Non-linear distortions are further divided into harmonic or non-harmonic distortion. In harmonic distortion all integer multiples of the fundamental frequency are considered. This is a classic distortion measurement called THD (Total Harmonic Distortion). In special applications, the total number of specific harmonics is considered.
Non-harmonic distortions are those frequencies that are not multiples of the fundamental frequency, as is the case with IMD (intermodulation distortion).