As a waveform passes through an audio or video system any deviation from the original signal is considered to be distortion. Therefore the output signal is no longer the same as the input signal only greater in amplitude, it has been changed and is now "distorted".

There are five different types of distortion:

1.    Frequency Distortion; occurs when only select frequencies are boost or cut unevenly across the audio spectrum. This variance (or lack there of) will be reflected in the specifications as the components Frequency Response.

2.    Phase Distortion; when any given frequency from a complex waveform takes longer to pass through a signal chain there is a phase shift in the individual frequencies. Even though their amplitudes may be amplified equally over the entire frequency band the compsite waveform has been varied.

3.    Total Harmonic Distortion (THD); the most commonly known form of distortion is directly related to the percentage of harmonics generated by the components in the signal chain. Measuring harmonic distortion is done using Fourier Analysis.

4.    Intermodulation (IM) Distortion; when an amplifier or system goes in to modulation combinations of spurious frequencies are generated. The combination of these new frequencies are equivalent to the sum and/or difference of integral multiples of the individual frequencies of a complex waveform.

5.    Transient Intermodulation (TIM); many solid-state amplifiers use abundant amounts of negative feedback in order to improve frequency response and reduction of harmonic distortion. During high-frequency music passages is when this distortion occurs.

by Jason Levert