An additional frequency in an audio signal derived from the fundamental or original frequency as a multiple of that fundamental that is smaller in amplitude (power) than the fundamental. Harmonics are distortions often found in audio reproduction and measured as THD or total harmonic distortion. fundamental of 2 kHz would have harmonics of 4 kHz (2 kHz times 2), 6 kHz (2 kHz time 3), 8 kHz (2 kHz times 4), 10 kHz (2 kHz times 5) and so on beyond audibility (human hearing is generally defined as being from 20 Hz to 20 kHz). Each harmonic is smaller than the original signal and smaller than the harmonic before it. This is similar to if you copied an original page on a copy machine at 90 percent. The copy would be smaller than (90 percent of) the original. Then say you copied the copy again at 90 percent. The second copy would still be a copy of the original page but would be even smaller than the first copy. Do it a third time and the third copy is again smaller but still a duplicate. Harmonics are similar in that they continue to decrease in size like a sloping hill; however, they are not exact copies of the original signal but multiples of it. hen purchasing audio equipment always look for low distortion. Try to locate equipment with harmonic distortion (THD) of 0.5% or less.