Updated

Total Harmonic Distortion Score and Tests
Headphones

What it is: The subtle, unwanted frequencies (harmonics) produced alongside the intended frequencies.
When it matters: When clean and pure sound reproduction is desired, though its effect is not as noticable as frequency response.
Score components:

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.

Test results

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.

Our tests


Distortion @ 90

What it is: The overall amount of harmonic distortion measured at 90dB SPL. To make the score more perceptually relevant, more weight is given to the higher frequencies.
When it matters: How pure the sound is at moderate listening levels.
Good value: <0.100
Noticeable difference: 0.1

[Coming soon]

 

Distortion @ 100

What it is: The overall amount of harmonic distortion measured at 100dB SPL. To make the score more perceptually relevant, more weight is given to the higher frequencies.
When it matters: How pure the sound is at loud listening levels.
Good value: <0.300
Noticeable difference: 0.1

[Coming soon]

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Questions & Answers

1 ANSWERED QUESTIONS
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Regarding your distortion measurements, specifically the parameters you set forth as targets, are you aware of the work of Geddes and Lee (available on their site, GedLee, under "distortion perception") and subsequently Olive and Welti (The Correlation between Distortion Audibility and Listener Preference in Headphones, available via the AES as well as on Listen Inc.'s site) on the matter? Have you considered measuring and displaying distortion via other methods, such as Olive and Welti's non-coherent distortion tests with music (which, in their test, correlated the most to individuals' preferences), or Geddes and Lee's GedLee metric?

Thanks for your message. We are familiar with Olive-Welti's paper, and have even discussed improving our measurements with them. As part of our new test bench, which will be rolled-out slowly over the next few months, we have an improved THD weight curve and have also added IMD measurements. But measuring non-coherent musical distortion may be a bit more difficult for us to implement at the moment.

The GedLee metric seems quite interesting! We've been thinking of something along the same line for a while, and are definitely open to incorporating it into our reviews, but it won't be a high priority at the moment. We have just finalized our new test bench, and based on the papers out there, we should first make sure we're getting our Frequency Response, Soundstage and Imaging right, before worrying about distortion! ;-)

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