Sound of harmonic distortion

One of the most basic and common ways to objectify the sound quality of an audio device is always its harmonic distortion. Harmonic distortion can be expressed by its total level (THD) or by the plot that shows its actual spectral content. But it remains a controversial topic. Some claim it is audible already at a 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.

And, no widely accepted theory about it has appeared so far. And hence, whether you believe it is the be-all and end-all of audio equipment quality, or nothing to care about, you can easily find supporting views.

That is the starting point here. However, for now, I will skip discussing this topic further and instead condense it as concisely as possible, moving it to a more practical level.

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

The audibility of harmonics will depend somewhat on your listening setup and your hearing abilities and skills. I myself would expect that, with a decent audio setup and average hearing, you may hear 5% second harmonic, and you will hardly hear it at 1%. Harmonics’ audibility will increase as their order increases, whether it is of odd or even order. So fourth and fifth harmonics 1% definitely won’t pass unnoticed. Then it takes to go to lower levels. Thus, the seventh harmonic (the critical one, according to some) is clearly audible at 1%, but it will be almost inaudible at 0.1%, and probably below the threshold when lowered further to 0.05%. The same 0.1% and 0.05% examples are also given for the fifteenth harmonic, which probably should go below 0.05% to get inaudible.

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

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

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

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

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