total harmonic distortion
- A measure of the distortion caused by all the harmonics present in an output signal which were not present in a sinusoidal input signal. It may be calculated as follows: the square of the ratio of the amplitude of the first harmonic to the fundamental frequency, and the square of the ratio of the second harmonic to the fundamental frequency, and so on are all added together, and the square root is taken from the result, and this number is then multiplied by 100 to express it as a percentage. This value is frequently used as an expression of the performance of audio components, especially amplifiers. Its abbreviation is THD.