What is MIDI?
The Musical Instrument Digital Interface (MIDI) enables people to use
multimedia computers and electronic musical instruments to create, enjoy
and learn about music. There are actually three components to MIDI, which
are the communications Protocol (language), the Connector (hardware
interface) and a distribution format called Standard MIDI Files.
Protocol
The MIDI protocol is an entire music description language in binary form.
Each word describing an action of musical performance is assigned a
specific binary code. MIDI was designed for keyboards, so many of the
actions are percussion oriented. To sound a note in MIDI language you send
a "Note On" message, and then assign that note a "velocity", which
determines how loud it plays. Other MIDI messages include selecting which
instrument to play, mixing and panning sounds, and controlling various
aspects of electronic musical instruments.
A table displaying many of the messages which make up the MIDI protocol is available for viewing from the Get Help with MIDI page on this site. For the complete protocol, you will need to get the most recent edition of the Complete MIDI 1.0 Detailed Specification.
Standard MIDI Files
When MIDI messages are stored on disks, they are commonly saved in the
Standard MIDI file format, which is slightly different from native MIDI
protocol, because the events are also time-stamped for playback in the
proper sequence. Music delivered by MIDI files is the most common use of
MIDI today. MIDI is the primary source of music in many popular PC games
and CD-ROM entertainment titles, and thousands of MIDI files are available
on the Internet for recreational use. Just about every personal computer is
now equipped to play Standard MIDI files.
One reason for the popularity of MIDI files is that, unlike digital audio files (.wav, .aiff, etc.) or even compact discs or cassettes, a MIDI file does not need to capture and store actual sounds. Instead, the MIDI file can be just a list of events which describe the specific steps that a soundcard or other playback device must take to generate ceratin sounds. This way, MIDI files are very much smaller than digital audio files, and the events are also editable, allowing the music to be rearranged, edited, even composed interactively, if desired.
With the recent introduction of the Downloadable Sounds format, MIDI files can also contain standardized samples of musical instruments, sound effects, or even dialogue, which are used to recreate an exact copy of the sound intended by the composer. MIDI files with DLS are the ideal solution for composers of all kinds who want the predictable playback of digital audio, but also need the compactness and/or interactivity of Standard MIDI Files for delivering their music.
What is GM?
In 1983 the MIDI (Musical Instrument Digital Interface) opened the door to communication between various musical instruments and computers.Compatibility at a basic level was consistent and reliable but each manufacture and each model used various technologies, and had varying features.
There had been a great variation in features of various sound generating devices, such as tone choices and locations, MIDI Channel assignments, etc.
The General MIDI System Level 1 (adopted in 1991) is a set of specifications for sound generating devices which has been agreed upon by both the Japanese MIDI Standards Committee (JMSC) and the American MIDI Manufacturers Association (MMA). These specifications seek to allow for the creation of music data which is not limited to equipment by a particular manufacturer or to specific models.
The General MIDI system defines data events such as the minimum number of voices that should correspond to which Program Change numbers, and the layout of Rhythm sounds on the Keyboard.Thanks to these specifications, any device that is equipped with sound sources supporting the General MIDI system will be able to accurately reproduce General MIDI Scores (Music Data created for the General MIDI System), regardless of the manufacture or the model.
What is GS?
The GS format is a set of specifications for sound sources which defines the
manner in which multi-timbral sound generating units will respond to MIDI messages.
The GS Format also complies with the General MIDI System.
The GS Format, from Roland, also defines a number of other details. These include unique specifications for sounds and the functions available for tone editing and effects (chorus and reverb), and other specifications concerning the manner in which sound sources will respond to MIDI messages. Any device that is equipped with GS Format sound source can faithfully reproduce GS Music Data (music data created under the GS format).
Roland fully supports General MIDI while providing the GS Format as a means to access compatibility and features beyond those specified within GM. General MIDI defines fundamental support to allow wide compatibility across a wide range of products. The more detailed definitions within the GS Format allow greater creative control for compatible sounds sources.