Sadly, There appears no practical way to convert audio files into MIDI files. There have been several brave attempts in shareware to do this, and I have tried a few, but none are any good I have found.
Simple one-note-at-a-time tunes, such as those played on a flute can usually be converted this way to MIDI. But the system fails when multiple-note chords are sounded, particularly complex chords. Present software systems have problems in unscrambling complex music and the results are chaotic.
If anyone has had success with this problem, I would be delighted to hear from them.
Best organic wishes for the New Year everyone!
Bob Essex
http://www.bobessex.co.uk