What is a MID File Type?
MID files are stored in a folder containing one or more audio files. A Guitar Hero audio track (recorded as a .OGG file) may have a corresponding MID file that contains guitar notes to play for that song.
Most players of rhythmic guitar will not need to open or delete MID files unless they want to modify notes or create their own song files. If you want to edit notes you can open and modify MID files using FeedBack and Moonscraper Chart Editor. Using the Guitar Hero Three Control Panel (GHTPC), you can import MID files directly into Guitar Hero III.
Also, guitar rhythmic files are saved with a .CHART file extension to avoid any confusion with standard MIDI files.
What is a Default MID File Name?
Notes.mid - The standard file name used to store rhythm data for a specific song.