Total harmonic distortion is a flaw in audio reproduction which deteriorates the music you listen to by generating frequencies that were not intended. This colors the expected sound and makes audio tracks sound impure and muddy.
There is more distortion produced at higher volumes but even then, it is still generally inaudible, except to very sensitive ears.
We tested for distortion at 90 dB SPL and at 100 dB SPL for the following headphones and ranked them by their overall distortion levels.
When it matters
At high levels of harmonic distortion, the audio you hear will have unintended frequencies, making it sound muddy and colored. Distortion is increased and more noticeable if you typically listen to music at higher volumes, or if the purity of audio reproduction is very important you.
However, it’s not a significant issue for most people and is rarely audible, except if distortion performance is very low or the listener has very sensitive ears.
Distortion @ 90
Distortion @ 100