Separate the song into its individual tracks, one track for each instrument. If you are working with live audio, or do not have access to the individual tracks, use your audio software to raise different instruments in the mix. Isolate their frequency range and use filters as necessary to remove as much of the other instruments as possible while maintaining the clarity of the original instrument. Save each track as a separate file in a WAV, AIFF or MP3 format.
Tune your audio conversion software, if necessary, by selecting the pitch from the Conversion menu. Convert each track to MIDI. After converting the track, listen to it with a MIDI player and confirm the notes, pitch and tone sound correct. Convert all your necessary tracks until you have the complete song in MIDI.
Create a new MIDI project in your audio editing software. Place each track on the time line as it was originally placed in the song. Create a track for the original song, and place it on the time line to allow you to properly align each track. Play back the project and the song to better align the MIDI tracks. After you are satisfied, remove the song from the project and export it as a Type 0 track, which combines all the instructions, and as a Type 1 track, which keeps each track separate, but will play back the instructions as a whole.