I have been doing some reading (for example at http://deposit.ddb.de/cgi-bin/dokserv?idn=972885544&dok_var=d1&dok_ext=pdf&filename=972885544.pdf) that indicates the nonlinear distortion products generated within the ear have been recorded for analysis. This would seem to imply that the ultimate limits to audio fidelity occur within the ear itself. I have been aware for some years of distortions that I hear in common among all playback systems no matter which system I am listening to. (I can only detect this with recordings that I know well, and I have not been able to hear it in live performance.) I have thought that this may represent the residual distortion level within my own ears. It is difficult to find data on distortion in normal hearing, since most work is intended to help those with hearing loss, but there is experimental evidence that significant levels of distortion are generated within the nonlinearities of normal (undamaged) hearing. This motivates the development of direct nerve interface electronics that avoid the nonlinear mechanical cochlear interface! That is one answer to another thread on "The Future of Loudpeakers", namely: no speaker at all!