On why THD numbers do not correlate well with perceived sound quality (PDF file) This is a graduate level thesis which was passed and approved by Electrical Engineering professors. It's based on the prior art of tests conducted by the BBC labs decades ago, the results & conclusions of which have unfortunately become lost for the most part in modern hi-fi. To briefly summarize, it's not the THD number which is important, rather, it's the distribution of the harmonic spectra...
...In short, TheVinylRipper should quit using Wikipedia and Google, and pick up some real actual textbooks and testing equipment. Norman Crowhearst's papers would be a good place to start.
what I really think of the Cheever thesis:
you may have to give up on the idea of the internet as an authoritative source in many scientific fields, JAES, ASA, in fact most peer reviewed journals don't put their content online for free, not that there isn't some good psychoacoustic info on the web:
...I think a highly relevant paper is “Coding High Quality Digital Audio” by a researcher at Meridian:
The paper is very technical (by head-fi standards at least, it is a “popularization” of a JAES convention paper) and the subject may seem a little off topic but in support of his argument for a particular coding scheme Stuart summarizes some of “conventional” audio engineering/psychoacoustic understanding of human perception limitations and their relation to reproduced audio – you might want to jump to the figures/graphs at the end of the paper and then search back into the text for the explanatory context
Some of the paper’s limits/thresholds of human audio perception would also be useful to consider in amplifier design as well as digital recording/playback
even Stereophile occasionally hints at some sophistication in distortion audibility discussion:
given the superior quality of of the above cited articles, (particularly the Czerwinski I cite a few posts down in the diyAudio thread) I'd really, really like to never see Cheever cited again