There are loads of wav-to-midi converters, mostly commercial:
http://www.akoff.com/
http://www.audioworks.com/
http://www.midi.ru/w2m/english/widi.htm
There seems to be remarkably little academic work in this area. I can't
understand why. But then I found this excellent item:
http://www.ece.cmu.edu/~ee551/projects/s_97_7/final.html
so maybe nobody else has anything to add!
Robin.
-- R.M.O'Leary <robin nospam at acm.org> +44 7010 7070 44, PO Box 20, Swansea SA2 8YB, UK