TL;DR

  1. Drag your MIDI file onto the Requester Chest, or click the chest and browse for a file.

  2. The settings page will list the tracks and instruments found in the MIDI file.

    If any notes are higher or lower than what their instrument can play, a red arrow and the number of notes will appear. These notes will not be heard in-game.

    You can attempt to fix these by either changing the Factorio instrument or by shifting the notes up or down - either from the instrument or the track.

    Please note that instruments and tracks contain the same set of notes: each note will get shifted by both it's instrument and track.

  3. Click Get Blueprint, and enjoy your new song!