audible distortion and tube gear?

@immatthewj The designer of the CD probably didn't understand what makes distortion audible to the ear. So they probably just added harmonics to the signal without doing anything else.

One of the things that makes distortion more audible (especially higher ordered harmonics) is if distortion rises with frequency, which is common in most amps with feedback but likely wasn't taken into account when the CD was created.

If you have hearing loss or other problems at the frequencies at which the distortion occurs, you might not hear it. But others around you might- if they are yelling at you to turn it down that's a clue. A good system never sounds loud until over 95dB or so. If it sounds loud below that you know you have a distortion problem of some sort.

I know that I have read on this site about "tube sound" having something to do with the way tube gear handles distortion, but would tube gear make it harder to recognize distortion?

@immatthewj Perhaps, depending on how much distortion your amp has and that of the speakers.

Distortion is mostly heard as a tonality, a change to the timbre of musical instruments. With a pure sine wave, higher orders added are easily heard since our ears use them to tell how loud sounds are (so are keenly sensitive to them); you need a bit more distortion for the lower orders (2nd and 3rd) to be audible.