MIDI file parsing homework

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1 Assignment

  1. Find a MIDI file on the web. Tip: include filetype:midior filetype:mid when searching for MIDI files in Google searches.
  2. 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.
  3. If it plays correctly, drag and drop the MIDI file from your desktop into the box below:
  4. 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.
  5. Parse at least 20 delta-time/message pairs in one of the tracks of the MIDI File. Note that type-1 files only stores 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.
  6. 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).
  7. 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).
  8. Decoding VLVs for delta timings is optional.
  9. 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.
  10. Extra Credit: Write your own Standard MIDI File parser which will do this homework for you.
  11. Email MIDI file and your parsing to you know whos.

2 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).