MIDI

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Musical Instrument Digital Interface
MIDI.png
Developer: Dave Smith
Header: SMF
Content: Notational
Instruments: Optional
Target Output
Output - Digital Audio - No.png Output - MIDI.png Output - FM Synthesis.png Output - PSG.png
Released: 1983-02-01
First Game: ?
Extensions
  • *.mid
  • *.midi
  • *.mff
  • *.smf
  • *.kar

Musical Instrument Digital Interface (MIDI) is a sound format created on 1 February 1983 by Dave Smith (1950-2022) of Sequential Circuits, Inc. in order to make a standard format for storing music definitions. Unlike PCM audio which stores the exact audio, or tracked audio that stores samples, MIDI doesn't store the any sound itself. Instead, MIDI stores the instructions for the audio (kind of like sheet music) which a MIDI device can play back. This allows for much smaller file sizes and consistent, exact timing. However, since all MIDI devices may synthesize sound differently, MIDI music will sound different everywhere it's played.

Most MIDI files are type 1, which means that they have a header for track information and allow multiple tracks. Some MIDI files are type 0, which don't support multiple tracks, and take up slightly less space. There is also a rarely seen type 2 MIDI file which is a type 1 MIDI file with several embedded type 0 MIDI tracks.

Some MIDI files use outdated extensions like MFF (MIDI File Format) or SMF (Standard MIDI File). The KAR extension is used by karaoke software, but is still a plain MIDI file.

Standards

MIDI itself is only a standard for a communication format between computers and other digital instruments. The mapping of MIDI "programs" to specific musical instruments was entirely dependent on the MIDI synthesizer. One of the most popular in computer gaming was the Roland MT-32, which appeared in 1987.

To provide a unified standard and avoid cacophony, the MIDI Manufacturer Association created the General MIDI standard in 1991 (often abbreviated GM). The majority of MIDI files are written for this standard. However, finding the standard quite limited and eager to compete by offering additional features, Roland and Yamaha both started to expand on the GM by developing their own proprietary but backward-compatible standards: the Roland GS and the Yamaha XG. Finally, the MMA released a "second level" to the General MIDI standard, called GM2, which is mostly derived from GS.

An XG, GS or GM2 synthesizer will play a GM MIDI file without problem. Inversely, a GM synthesizer will usually play an XG, GS or GM2 file without much loss beyond a few special effects, although it is possible that they use more simultaneous voices than what the GM standard offers, or undefined instruments. (The XG standard offers up to 1149 different instruments and 128 simultaneous voices; GM is limited to 128 instruments and 24 simultaneous voices.)

However, a MT-32 synthesizer playing a GM song, or a GM synthesizer playing an MT-32 song, will produce fundamentally incorrect playback as the instruments are mapped differently.

In addition to the features offered by the various standards, some sound cards offered additional functions, such as the possibilities to reprogram instruments. Of particular importance are the AdLib and SoundBlaster cards and the Gravis UltraSound (abbreviated GUS) cards.

The AdLib offered FM synthesis with its YM3812 sound chip (better known as OPL2). The OPL2 chip could be reprogrammed by changing the values in its registers to modify the sounds produced. Ad Lib Inc. created MDI derivative format for this purpose.

The GUS used a system of "instrument patches" containing instrument samples to offer high-quality MIDI playback. However, the limited RAM on-board the card made it impossible to give each General MIDI instrument its own patch simultaneously. To reduce memory use, configuration files (ultramid.ini) were used to remap instrument to similar patches, making it necessary to optimize such configurations for the instruments used in the songs played. But it was possible to use custom patches, either to improve the quality of certain instruments, or make the patches smaller so more of them could be loaded at once, or even provide entirely new custom instruments.

Many games included multiple variants of their MIDI soundtracks, offering for example an MT-32 version, a GM OPL2 version and a GM wave table version.

For all these reasons, there exist OPL emulators, GUS emulators, and MT-32 emulators in addition to generic MIDI players.

Karaoke files

The .kar format was originally developed by Tune 1000 for a commercial product (Soft Karaoke, 1993). It's still widely used today for karaoke MIDI files, even though it was never approved by the MMA.

The first track contains text events that are used to make the file recognizable by the program as a Soft Karaoke file. "@KMIDI KARAOKE FILE" text event specifies that this is the Soft Karaoke file. Anything starting with @I is any information about the file.

The second track contains the text events for the lyrics of the song. The first event is "@LENGL", which identifies the language the words are in, which is English. The next couple of event start with "@T" which identifies the title and metadata of the song. Example: "@TNever Gonna Give You Up"

The rest of the second track contains the words of the song. If the text event starts with "\", it means to clear the screen and show the words at the top of the screen. If it starts with "/", it means a new line.

Some karaoke programs extract part of the "@T" information. It is a good idea to put the song title on the first "@T" line, and to put the artist on the second "@T" line. This way these programs will display the information in the 'Title' and 'Artist' columns in their directory window.

Players

(Category)

Editors

(Category)

Converters

(Category)

MIDI to ?

? to MIDI

Games

(Category)

These are 20 of the more popular games that use MIDI, for the complete list, view the category.

Released Title Sample
1990-09-?? Prince of Persia (DOS)
1991-09-19 Wordtris (DOS)
1991-10-?? Windows 3 (DOS)
1991-??-?? Baby Jo In Going Home (DOS)
1991-??-?? SimAnt (DOS)
1991-??-?? Super Tetris (DOS)
1991-??-?? Where In the World Is Carmen Sandiego?: 1991 Edition (DOS)
1992-??-?? A-Train (DOS)
1992-??-?? Chip's Challenge (W16)
1992-??-?? SimCity (W16)
1992-??-?? SimLife (W16)
1994-02-19 Pirates! Gold (W16)
1994-10-17 Wacky Wheels (DOS)
1994-12-21 Rise of the Triad: Dark War (DOS)
1995-09-30 Monopoly (W16)
1996-??-?? The Elder Scrolls II: Daggerfall (DOS)
1996-??-?? SimFarm (W16)
1997-05-31 Blood (DOS)
1997-10-15 Age of Empires (W32)
1999-09-30 Age of Empires II: The Age of Kings (W32)

How to Obtain

MIDI files usually have to be manually extracted from game files, a process that is different for pretty much every game that uses them. A lot of free MIDI files can also be found online, for various covers of songs or even original compositions.

Technical

All MIDI files begin with "MThd" which is the start of the MIDI header. There may also be sub-headers in the MIDI file. Inside each header there will be a "MTrk" which signifies the beginning of a track. Type-0 MIDI files only have 1 track, but type-1 files may contain multiple tracks. There is also type-2 which can contain separate sequences that do not have to play simultaneously, however it's extremely rare and rarely supported.

All properly formatted MIDI files should end with same three bytes, 0xFF 0x2F 0x00 (the EndOfTrack meta event)

MIDI can have a minimum tempo of 16 BPM and a maximum of 500 BPM. The tempo may be decimal and multiple tempo changes per second are allowed for smooth slowdowns and speed-ups.

Links

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