Screw high order harmonic distortion. Harmonic distortion is related to the signal itself. IM distortion is, by definition, enharmonic, and much worse. Many factors contribute to sweet sound, frequency response, harmonic distortion spectra, amp behavior at clipping, room treatment, etc., but a lack of IM distortion is certainly one of them.
What makes strings sound "sweet"?
I have always wondered about this. If you listen to many recordings of bowed string instruments, then you know that the upper registers can sometimes have a sweet tone. I define this by what it is not - edgy, brittle, dry and rough sounding. It is smooth and inviting. I used to assume this was due to rolled off highs or an emphasized midrange, but I am not so sure. It varies by recording, or course, but I have often wondered what, in the recording or reproduction process, causes strings to either sound brittle or sweet. Is it the acoustic of the original recording venue? A frequency balance issue? I would love to hear from those who might know. Thanks!