MIDI file parsing homework
Assignment
- Find a MIDI file on the web. Tip: include filetype:midior filetype:mid when searching for MIDI files in Google searches.
- Save the MIDI file to your desktop and open it (usually double-clicking to open with the default MIDI playing program on your computer). Here are instructions for installing an older version of Quicktime in OS X which plays MIDI files.
- If it plays correctly, drag and drop the MIDI file from your desktop into the box below:
- Parse the resulting display of the MIDI file's hexadecimal bytes by hand. Make note of the number of tracks in the file; whether it is type-0 or type-1 (or type-2), and how many ticks per quarter note are used for basic timing in the file.
- Parse at least 20 delta-time/message pairs in one of the tracks of the MIDI File. Note that type-1 files only store meta messages such as tempo changes in the first track. If your file is a type-1 file, try parsing a few of these meta messages, and then switch to another track with notes.
- Give the basic meaning of MIDI messages (such as this is a note-on messages for pitch A4, or this is a tempo meta message).
- Does the MIDI file use "running status"? Running status would result in the first byte of a MIDI message in any (delta-time/message) pair to be a data byte rather than a command-byte (and the last command-byte in the track would be the inferred command byte).
- Decoding VLVs for delta timings is optional.
- Extra Credit: If decoding the VLV values, does the MIDI file look like it was performed live, or does it represent quantized/proportional time? In other words, if the ratio of time values looks like integers, such as 2:1 for quarter-note:eighth note, then it could not possibly be performed so accurately.
- Extra Credit: Write your own Standard MIDI File parser which will do this homework for you.
- Email MIDI file and your parsing to you-know-whos.
Example
Here is the simple example done in class using File:Twinkle.mid:
4d 54 68 64 00 00 00 06 00 00 00 01 00 80 4d 54 72 6b 00 00 00 8c 00 ff 58 04 04 02 30 08 00 ff 59 02 00 00 00 90 3c 28 81 00 90 3c 00 00 90 3c 1e 81 00 90 3c 00 00 90 43 2d 81 00 90 43 00 00 90 43 32 81 00 90 43 00 00 90 45 2d 81 00 90 45 00 00 90 45 32 81 00 90 45 00 00 90 43 23 82 00 90 43 00 00 90 41 32 81 00 90 41 00 00 90 41 2d 81 00 90 41 00 00 90 40 32 40 90 40 00 40 90 40 28 40 90 40 00 40 90 3e 2d 40 90 3e 00 40 90 3e 32 40 90 3e 00 40 90 3c 1e 82 00 90 3c 00 00 ff 2f 00
Basic parsing:
4d 54 68 64 ; ASCII characters "MThd"
00 00 00 06 ; Number of bytes in header to follow: 6
00 00 ; MIDI file type: 0
00 01 ; Number of tracks: 1
00 80 ; Ticks per quarter note: 128
4d 54 72 6b ; ASCII characters "MTrk"
00 00 00 8c ; Number of bytes in track to follow: 140
00 ; 0 ticks
ff 58 04 04 02 30 08 ; time signature meta event
00 ; 0 ticks
ff 59 02 00 00 ; key signature meta event
00 ; 0 ticks
90 3c 28 ; note-on C4
81 00 ; 128 ticks
90 3c 00 ; note off C4
00 ; 0 ticks
90 3c 1e ; note-on C4
81 00 ; 128 ticks
90 3c 00 ; note off C4
00 ; 0 ticks
90 43 2d ; note-on
81 00 ; 128 ticks
90 43 00 ; note-off
00 ; 0 ticks
90 43 32 ; note-on
81 00 ; 128 ticks
90 43 00 ; note-off
00 ; 0 ticks
90 45 2d ; note-on
81 00 ; 128 ticks
90 45 00 ; note-off
00 ; 0 ticks
90 45 32 ; note-on
81 00 ; 128 ticks
90 45 00 ; note-off
00 ; 0 ticks
90 43 23 ; note-on
82 00 ; 256 ticks
90 43 00 ; note-off
00 ; 0 ticks
90 41 32 ; note-on
81 00 ; 128 ticks
90 41 00 ; note-off
00 ; 0 ticks
90 41 2d ; note-on
81 00 ; 128 ticks
90 41 00 ; note-off
00 ; 0 ticks
90 40 32 ; note-on
40 ; 64 ticks
90 40 00 ; note-off
40 ; 64 ticks
90 40 28 ; note-on
40 ; 64 ticks
90 40 00 ; note-off
40 ; 64 ticks
90 3e 2d ; note-on
40 ; 64 ticks
90 3e 00 ; note-off
40 ; 64 ticks
90 3e 32 ; note-on
40 ; 64 ticks
90 3e 00 ; note-off
40 ; 64 ticks
90 3c 1e ; note-on
82 00 ; 256 ticks
90 3c 00 ; note-off
00 ; 0 ticks
ff 2f 00
Example of more detailed parsing:
4d 54 68 64 MIDI header chunk marker ("MThd")
00 00 00 06 Bytes to follow in header chunk (6)
00 00 file format: Type-0 (0 == single track format)
00 01 number of tracks (1)
00 80 ticks per quarter note (128)
First (and only track):
4d 54 72 6b MIDI track chunk marker ("MTrk")
00 00 00 8c Bytes to follow in track chunk (140 bytes)
Delta time / MIDI message
============================================
0 ff 58 '4 4 2 30 8 Meta-message for time signature 4/; 48 ticks per metronome click; 8 32nds per beat
0 ff 59 '2 0 0 Meta-message for key signature: C major
0 90 '60 '40 Note on, C4
128 90 '60 0 Note off, C4
0 90 '60 '30 etc.
128 90 '60 0
0 90 '67 '45
128 90 '67 0
0 90 '67 '50
128 90 '67 0
0 90 '69 '45
128 90 '69 0
0 90 '69 '50
128 90 '69 0
0 90 '67 '35
256 90 '67 0
0 90 '65 '50
128 90 '65 0
0 90 '65 '45
128 90 '65 0
0 90 '64 '50
64 90 '64 0
64 90 '64 '40
64 90 '64 0
64 90 '62 '45
64 90 '62 0
64 90 '62 '50
64 90 '62 0
64 90 '60 '30
256 90 '60 0
0 ff 2f 0 Meta-message for end-of-track
Notice that this MIDI file was clearly not performed live. The delta-time durations are: 0, 64, 128, and 265 which are all multiples of two from each other (representing eighth notes, quarter notes and half notes).