here’s a discussion on how to detect and eliminate xing encoded mp3s. the title is great: Program to delete Xing encoded mp3s?
also here’s a thread on testing your hearing frequency (with audio files and methodology.
points to pcabx, a free program written by arny krueger, of pcavtech fame. pretty neat. there’s an listening training section for audio-technical training. also, and this is interesting, there’s also a page on musical-artistic listening. it’s amazing to be actively surfing the net for over five years, and still finding incredible useful stuff.