[AstralStorm]

Unfortunately, your wild guess does not fit experience.

Second partially true (as validated by intersubjective tests) guess is that the harmonic structure matters. It is a major component of the coloration, and funnily enough low non-tapering one is discernible from low tapering one despite what SINAD/THD graphs suggest. Amount is discernible too, especially of second and third harmonic, and total of higher harmonics, but we have not established the thresholds. And for lower harmonics, mostly at lower volumes unless it's a lot. Intermodulating injected ultrasound medium to high level garbage (as produced by some poorly implemented power supplies in bad PSRR amps) is sometimes detectable and tests tend to miss it. It also sounds different from just bad SINAD/IMD. Crossover distortion also sounds pretty bad especially at low volumes.

AES researchers (Earl Geddes, Lidia Lee, 2003) tried for a better perceptually weighted harmonic and intermodulation distortion metric in the past. It went nowhere because industry always wins. Even that is only a part of the answer.

And if the amplifier does outright clip, either in current or in voltage, that sounds just rough.

[nimish]

That's why SINAD is good, low enough sinad and the spur distribution irrelevant.

You arent going to hear intermodulation distortion at -110dBfs regardless of how you weight it.

I want zero distortion or as close to it, not euphonic distortion unless I put it in there via equalization or effects or whatever.