Total Harmonic Distortion
From Zanecorpwiki
Total harmonic distortion is a measure of the distortion added by harmonics introduced by components in an audio path.[1] A harmonic is a signal whose frequency is a integral (whole number) multiple of the primary frequency.[2] In other words, if you had a signal at 2KHz, the first harmonic would be a 4KHz signal, which would presumably have much less power (amplitude). What we hear is the sum of the primary signal and all the harmonic signals... hence, the total harmonic distortion.
As discussed in the Amplifier Distortion article, THD is pretty much a solved problem.
