Term: THD

Total Harmonic Distortion: when the harmonic distortion of a device is tested, the appearance of new frequencies that have been added to the original frequency to be transmitted by a device is measured. These frequencies (derived from the fundamental frequency generated) are undesirable because they are modifying the original signal.
Total harmonic distortion is the sum of all harmonics measured in the frequency band of the audio device in question, more noise.
The optimal value is ≤ 0.01% distortion, while a value of 1% distortion is intolerable value.