Sound of harmonic distortion

One of the basic and most common ways to objectify sound qualities of audio device was always its harmonic distortion. Harmonic distortion can be given by its total level (THD), or by the plot that shows its actual spectral content. But it remains controversial topic. Some claim it is audible yet at very low level, but others say it is inaudible even when it reaches quite high amounts. Sometimes, harmonic distortion is discussed with regard to its more or less audible components, and their more or less “dis-harmonic” effects, subjectively speaking. But no theory about it appeared widely accepted so far. So whether you believe it is be-all and end-all of audio equipment quality, or nothing to really care about, you can easily find supporting views.

That is the starting point here. But for now I will skip discussing further this topics, and instead I will cut a long story as short and effective as possible, and move it to a rather practical level.

So, below you will find several examples of distorted sinewave. You will firstly find pure sinewave, and then the same sinewave distorted by different harmonic components. I used 500 Hz basic frequency instead of usual 1 kHz, so quite high order harmonics remained inside the audio band.

Harmonics audibility will depend somewhat on your listening setup, and on your hearing abilities and skills. With decent audio setup and average hearing you may hear 5% second harmonic, but you will hardly hear it at 1%. Harmonics audibility will increase as their order increases, and probably there will be no matter if it is odd or even order. So fourth and fifth harmonics 1% definitely won’t pass unnoticed. Then it takes to go to lower levels.  Thus seventh harmonic (according to some, it is the critical one) is clearly audible at 1%, but it will get almost inaudible at 0.1%, and probably below threshold when lowered further to 0.05%. The same 0.1% and 0.05% examples are also given for fifteenth harmonic, which probably should go below 0.05% to get inaudible.

But again, it is up to you to listen to the examples and check what you hear, and get your own sense of this.

(If your web browser or audio hardware do not support 24 bit playback, please scroll down.)




As for my bottom line, it is the one of rather general kind:

Any attempt of getting across “objective” knowledge is faced with impossibility to avoid own perspective. The point of view is, and remains a fact of view. Still, this doesn’t make any knowledge impossible or invalid. Nor do all views are equal. The problem with point of view is not in having one, but in being unaware of it, or not acting accordingly. Oh yes, being aware of it also helps possibly correcting it, and moving to better position.

The other topics like “does harmonic distortion have smearing effects even when it is not directly audible?” I will leave for some other day.


Added on 25.05.2015:

In addition to the above examples, which are 24 bit files that play nicely in web browsers such as Chrome, here are the same files reduced down to 16 bits. Unfortunately not all browsers support all bit depths, for instance playback in Firefox is still limited to 16 bit. Bit depth is reduced by the use of dither and noise shaping, which are very useful and effective in this case, so I believe the conclusions will be the same with both above and these examples.