Tutorial: The Technology of MIDI

MIDI Cables & Connectors
MIDI Messages
Standard MIDI Files

Playing a musical instrument can provide a lifetime of enjoyment and friendship. Whether your goal is to play in a band, or you just want to perform privately in your home, or you want to develop your skills as a music composer or arranger, MIDI can help.

There are many different kinds of devices that use MIDI, from cell phones to music keyboards to personal computers. The one thing all MIDI devices have in common is that they speak the "language" of MIDI. This language describes the process of playing music in much the same manner as sheet music: there are MIDI Messages that describe what notes are to be played and for how long, as well as the tempo, which instruments are to be played, and at what relative volumes. 

Because MIDI data is only performance instructions and not a digital version of a sound recording, it is actually possible to change the performance, whether that means changing just one note played incorrectly, or changing all of them to perform the song in an entirely new key or at a different tempo, or on different instruments. 

MIDI data can be transmitted electronically between MIDI-compatible musical instruments, or stored in a Standard MIDI File for later playback. In either case, the resulting performance will depend on how the receiving device interprets the performance instructions, just as it would in the case of a human performer reading sheet music. The ability to fix, change, add, remove, speed up or slow down any part of a musical performance is exactly why MIDI is so valuable for creating, playing and learning about music.

Three Kinds of MIDI

The original Musical Instrument Digital Interface (MIDI) specification defined a physical connector and message format for connecting devices and controlling them in "real time". A few years later Standard MIDI Files were developed as a storage format so performance information could be recalled at a later date. The three parts of MIDI are often just referred to as "MIDI ", even though they are distinctly different parts with different characteristics.

The MIDI Messages specification (or "MIDI Protocol") is probably the most important part of MIDI. Though originally intended just for use with the MIDI DIN transport (see Part 2) as a means to connect two keyboards, MIDI messages are now used inside computers and cell phones to generate music, and transported over any number of professional and consumer interfaces (USB, FireWire, etc.) to a wide variety of MIDI-equipped devices. There are different message groups for different applications, only some of which are we able to explain here. (Part 2)

There are also many different Cables & Connectors that are used to transport MIDI data between devices. The "MIDI DIN" transport causes a lot of confusion because it  has specific characteristics which some people associate as characteristics of "MIDI" -- forgetting that the MIDI-DIN characteristics go away when using MIDI over other transports (and inside a computer). With computers a High Speed Serial, USB or FireWire connection is more common. Each transport has its own performance characteristics which might make some difference in specific applications, but in general the transport is the least important part of MIDI, as long as it allows you to connect all the devices you want use! (Part 3)

The final part of MIDI are the Standard MIDI Files (and variants), which are used to distribute music playable on MIDI players of both the hardware and software variety. All popular computer platforms can play MIDI files (*.mid) and there are thousands of web sites offering files for sale or even for free. Anyone can make a MIDI file using commercial (or free) software that is readily available, and many people do, with a wide variety of results. Whether or not you like a specific MIDI file can depend on how well it was created, and how accurately your synthesizer plays the file... not all synthesizers are the same, and unless yours is similar to that of the file composer, what you hear may not be at all what he or she intended. (Part 4)

Even More MIDI

Over the past 20 years MMA member companies have created many extensions and enhancements to MIDI that are designed to address some of the issues mentioned briefly above. General MIDI (GM) and Downloadable Sounds (DLS) help address the issue of predictable playback from MIDI Files. Scalable Polyphony MIDI helped bring MIDI to mobile phones by providing a standard means for scaling playback of complex MIDI files across a variety of low-power handsets. More information on extensions and enhancements are available throughout this web site, especially in the TechSpecs area. 

Many people today see MIDI as a way to accomplish something, rather than as a protocol, cable, or file format. For example, many musicians will say they "use MIDI", "compose in MIDI" or "create MIDI parts", which means they are sequencing MIDI events for playback via a synthesizer, rather than recording the audio that the synthesizer creates.