Total harmonic distortion

Total Harmonic Distortion, the English name Total Harmonic Distortion, referred to as THD. Before explaining the total harmonic distortion, let's first understand what harmonic distortion is.

Harmonic distortion refers to the distortion of the speaker when it plays back sound due to resonance phenomenon during the operation of the speaker. Although only the baseband signal is the original signal of the sound in the cabinet, it is inevitable that there will be a resonance phenomenon (second, third or even more harmonics are generated on the basis of the original sound wave), so that there is no longer only a sound signal. The baseband signal, but also includes harmonics and their frequency multiplication components, these frequency multiplication signals will cause the speaker to produce distortion when playing. For ordinary speakers, certain harmonic signal components are allowed to exist, but it must be based on the premise that there is no major influence on the output of the fundamental signal of the sound.

Total harmonic distortion refers to the additional harmonic components of the output signal (harmonics and harmonic components thereof) that are greater than the input signal when input from the signal source, and is usually expressed as a percentage. In general, the total harmonic distortion at the frequency of 1000 Hz is minimal, so many products use the distortion of this frequency as its index. So when testing total harmonic distortion, a 1000Hz sound is emitted to detect it. The smaller the value, the better.

Note: The total harmonic distortion of some datasheets is expressed as THD < 0.5%, 1W, so it seems that the total harmonic distortion is small, but only in the total harmonic distortion of the output power of 1W, which is under the measurement conditions required by the standard The resulting total harmonic distortion is different. Therefore, when evaluating MP3's total harmonic distortion index, it should be noted under what conditions.