Scott
The T4 converter you are thinking of is the other way around. It will play a MIDI file while it records the output of the sound engine to an MP3 file, basically just a simple internal sound recording. The conversion you seek is a whole different technology. WAV, MP3, AIFF, etc files are actual sound files or sound recordings. They may be digitized, but they are still actual sound recordings. MIDI files are nothing more than a set of instructions (program) that tell the sound engine what to do - what key was pressed when and for how long and how hard was it hit and how hard was it pressed after it hit bottom, etc. It is sort of an elaborate electronic equivalent to a paper song roll for a player piano. Both cause some other device to make a tune, but neither can be considered actual SOUND. Converting a sound file to a MIDI file requires software known as a pitch-to MIDI converter, but they do have their drawbacks and many are disappointed at their results. They seem to work best with single note tunes, as multiple tones and chords tend to confuse them. I did come across one that claims to have polyphonic capabilities, if you are interested:
http://www.intelliscore.net/Good luck !
Regards,
Ted