here a small amount of URL about this topic - I think very interested for some members
http://www.gedlee.com/downloads/Distortion_AES_I.pdf
http://www.gedlee.com/downloads/Distortion_AES_II.pdf
http://www.gedlee.com/downloads/AES06Gedlee_ll.pdf
http://projekter.aau.dk/projekter/fbspretrieve/9852082/07gr1061_Thesis.pdf
http://www.sea-acustica.es/WEB_ICA_07/fchrs/papers/ppa-04-007.pdf
Stereophile: Euphonic Distortion: Naughty but Nice?
http://www.gedlee.com/downloads/Distortion_AES_I.pdf
http://www.gedlee.com/downloads/Distortion_AES_II.pdf
http://www.gedlee.com/downloads/AES06Gedlee_ll.pdf
http://projekter.aau.dk/projekter/fbspretrieve/9852082/07gr1061_Thesis.pdf
http://www.sea-acustica.es/WEB_ICA_07/fchrs/papers/ppa-04-007.pdf
Stereophile: Euphonic Distortion: Naughty but Nice?