MIDI (/หmษชdi/; short for Musical Instrument Digital Interface) is a technical standard that describes a protocol, digital interface and connectors and allows a wide variety of electronic musical instruments, computers and other related devices to connect and communicate with one another. A single MIDI link can carry up to sixteen channels of information, each of which can be routed to a separate device.
MIDI carries event messages that specify notation, pitch and velocity, control signals for parameters such as volume, vibrato, audio panning, cues, and clock signals that set and synchronize tempo between multiple devices. These messages are sent via a MIDI cable to other devices where they control sound generation and other features. This data can also be recorded into a hardware or software device called a sequencer, which can be used to edit the data and to play it back at a later time.
The MIDI technology was standardized in 1983 by a panel of music industry representatives, and is maintained by the MIDI Manufacturers Association (MMA). All official MIDI standards are jointly developed and published by the MMA in Los Angeles, California, US, and for Japan, the MIDI Committee of the Association of Musical Electronics Industry (AMEI) in Tokyo.
Advantages of MIDI include compactness (an entire song can be coded in a few hundred lines, i.e. in a few kilobytes), ease of modification and manipulation and choice of instruments.
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| MIDI allows multiple instruments to be played from a single controller (often a keyboard, as pictured here), which makes stage setups much more portable. This system fits into a single rack case, but prior to the advent of MIDI would have required four separate full-size keyboard instruments, plus outboard mixing and effects units. |
Instrument control
MIDI was invented so that musical instruments could communicate with each other and so that one instrument can control another. Analog synthesizers that have no digital component and were built prior to MIDI's development can be retrofit with kits that convert MIDI messages into analog control voltages. When a note is played on a MIDI instrument, it generates a digital signal that can be used to trigger a note on another instrument. The capability for remote control allows full-sized instruments to be replaced with smaller sound modules, and allows musicians to combine instruments to achieve a fuller sound, or to create combinations such as acoustic piano and strings. MIDI also enables other instrument parameters to be controlled remotely. Synthesizers and samplers contain various tools for shaping a sound. Filters adjust timbre, and envelopes automate the way a sound evolves over time. The frequency of a filter and the envelope attack, or the time it takes for a sound to reach its maximum level, are examples of synthesizer parameters, and can be controlled remotely through MIDI. Effects devices have different parameters, such as delay feedback or reverb time. When a MIDI continuous controller number is assigned to one of these parameters, the device will respond to any messages it receives that are identified by that number. Controls such as knobs, switches, and pedals can be used to send these messages. A set of adjusted parameters can be saved to a device's internal memory as a "patch", and these patches can be remotely selected by MIDI program changes. The MIDI standard allows selection of 128 different programs, but devices can provide more by arranging their patches into banks of 128 programs each, and combining a program change message with a bank select message.
Composition
MIDI events can be sequenced with computer software, or in specialized hardware music workstations. Many digital audio workstations (DAWs) are specifically designed to work with MIDI as an integral component. MIDI piano rolls have been developed in many DAWs so that the recorded MIDI messages can be extensively modified. These tools allow composers to audition and edit their work much more quickly and efficiently than did older solutions, such as multi-track recording. They improve the efficiency of composers who lack strong pianistic abilities, and allow untrained individuals the opportunity to create polished arrangements.
Because MIDI is a set of commands that create sound, MIDI sequences can be manipulated in ways that prerecorded audio cannot. It is possible to change the key, instrumentation or tempo of a MIDI arrangement, and to reorder its individual sections. The ability to compose ideas and quickly hear them played back enables composers to experiment. Algorithmic composition programs provide computer-generated performances that can be used as song ideas or accompaniment.
Some composers may take advantage of MIDI 1.0 and General MIDI (GM) technology to allow musical data files to be shared among various electronic instruments by using a standard, portable set of commands and parameters. The data composed via the sequenced MIDI recordings can be saved as a Standard MIDI File (SMF), digitally distributed, and reproduced by any computer or electronic instrument that also adheres to the same MIDI, GM, and SMF standards. MIDI data files are much smaller than recorded audio files.
MIDI and computers
At the time of MIDI's introduction, the computing industry was mainly devoted to mainframe computers, and personal computers were not commonly owned. The personal computer market stabilized at the same time that MIDI appeared, and computers became a viable option for music production. In the years immediately after the 1983 ratification of the MIDI specification, MIDI features were adapted to several early computer platforms, including Apple II Plus, IIe and Macintosh, Commodore 64 and Amiga, Atari ST, Acorn Archimedes, and PC DOS. The Macintosh was the favorite among US musicians, as it was marketed at a competitive price, and would be several years before PC systems would catch up to its efficiency and graphical interface. The Atari ST was favored in Europe, where Macintoshes were more expensive. The Apple IIGS used a digital sound chip designed for the Ensoniq Mirage synthesizer, and later models used a custom sound system and upgraded processors, which drove other companies to improve their own offerings. The Atari ST was favored for its MIDI ports that were built directly into the computer. Most music software in MIDI's first decade was published for either the Apple or the Atari. By the time of Windows 3.0's 1990 release, PCs had caught up in processing power and had acquired a graphical interface, and software titles began to see release on multiple platforms.
Standard MIDI files
The Standard MIDI File (SMF) is a file format that provides a standardized way for sequences to be saved, transported, and opened in other systems. The compact size of these files has led to their widespread use in computers, mobile phone ringtones, webpage authoring and greeting cards. They are intended for universal use, and include such information as note values, timing and track names. Lyrics may be included as metadata, and can be displayed by karaoke machines. The SMF specification was developed and is maintained by the MMA. SMFs are created as an export format of software sequencers or hardware workstations. They organize MIDI messages into one or more parallel tracks, and timestamp the events so that they can be played back in sequence. A header contains the arrangement's track count, tempo and which of three SMF formats the file is in. A type 0 file contains the entire performance, merged onto a single track, while type 1 files may contain any number of tracks that are performed in synchrony. Type 2 files are rarely used and store multiple arrangements, with each arrangement having its own track and intended to be played in sequence. Microsoft Windows bundles SMFs together with Downloadable Sounds (DLS) in a Resource Interchange File Format (RIFF) wrapper, as RMID files with a .rmi extension. RIFF-RMID has been deprecated in favor of Extensible Music Files (XMF).
File sharing
A MIDI file is not a recording of actual audio. Rather, it is a set of instructions, and can use a thousand times less disk space than the equivalent recorded audio. This made MIDI file arrangements an attractive way to share music, before the advent of broadband internet access and multi-gigabyte hard drives. Licensed MIDI files on floppy disks were commonly available in stores in Europe and Japan during the 1990s. The major drawback to this is the wide variation in quality of users' audio cards, and in the actual audio contained as samples or synthesized sound in the card that the MIDI data only refers to symbolically. Even a sound card that contains high-quality sampled sounds can have inconsistent quality from one instrument to another, while different model cards have no guarantee of consistent sound of the same instrument. Early budget cards, such as the AdLib and the Sound Blaster and its compatibles, used a stripped-down version of Yamaha's frequency modulation synthesis (FM synthesis) technology played back through low-quality digital-to-analog converters. The low-fidelity reproduction of these ubiquitous cards was often assumed to somehow be a property of MIDI itself. This created a perception of MIDI as low-quality audio, while in reality MIDI itself contains no sound, and the quality of its playback depends entirely on the quality of the sound-producing device (and of samples in the device).
MIDI software
The main advantage of the personal computer in a MIDI system is that it can serve a number of different purposes, depending on the software that is loaded. Multitasking allows simultaneous operation of programs that may be able to share data with each other.
See: Comparison of MIDI editors and sequencers
Sequencers
Sequencing software provides a number of benefits to a composer or arranger. It allows recorded MIDI to be manipulated using standard computer editing features such as cut, copy and paste and drag and drop. Keyboard shortcuts can be used to streamline workflow, and editing functions are often selectable via MIDI commands. The sequencer allows each channel to be set to play a different sound, and gives a graphical overview of the arrangement. A variety of editing tools are made available, including a notation display that can be used to create printed parts for musicians. Tools such as looping, quantization, randomization, and transposition simplify the arranging process. Beat creation is simplified, and groove templates can be used to duplicate another track's rhythmic feel. Realistic expression can be added through the manipulation of real-time controllers. Mixing can be performed, and MIDI can be synchronized with recorded audio and video tracks. Work can be saved, and transported between different computers or studios.
Sequencers may take alternate forms, such as drum pattern editors that allow users to create beats by clicking on pattern grids, and loop sequencers such as ACID Pro, which allow MIDI to be combined with prerecorded audio loops whose tempos and keys are matched to each other. Cue list sequencing is used to trigger dialogue, sound effect, and music cues in stage and broadcast production.
Notation/scoring software
With MIDI, notes played on a keyboard can automatically be transcribed to sheet music. Scorewriting software typically lacks advanced sequencing tools, and is optimized for the creation of a neat, professional printout designed for live instrumentalists. These programs provide support for dynamics and expression markings, chord and lyric display, and complex score styles. Software is available that can print scores in braille.
ScoreCloud is software that can transcribe from MIDI to scores in real time. SmartScore software performs the reverse process and can produce MIDI files from scanned sheet music. Other notation programs include Finale, Encore and Sibelius.
Game music
Early PC games were distributed on floppy disks, and the small size of MIDI files made them a viable means of providing soundtracks. Games of the DOS and early Windows eras typically required compatibility with either Ad Lib or SoundBlaster audio cards. These cards used FM synthesis, which generates sound through modulation of sine waves. John Chowning, the technique's pioneer, theorized that the technology would be capable of accurate recreation of any sound if enough sine waves were used, but budget computer audio cards performed FM synthesis with only two sine waves. Combined with the cards' 8-bit audio, this resulted in a sound described as "artificial" and "primitive". Wavetable daughterboards that were later available provided audio samples that could be used in place of the FM sound. These were expensive, but often used the sounds from respected MIDI instruments such as the E-mu Proteus. The computer industry moved in the mid-1990s toward wavetable-based soundcards with 16-bit playback, but standardized on a 2MB ROM, a space too small in which to fit good-quality samples of 128 instruments plus drum kits. Some manufacturers used 12-bit samples, and padded those to 16 bits. The N64 was cabable of playing MIDI music, Doom 64 used the format to save space on the cartridge. Today, it is uncommon for developers to use MIDI for their games.
See: MIDI in video games.
MIDI Devices and connectors.
The cables terminate in a 180° five-pin DIN connector. Standard applications use only three of the five conductors: a ground wire, and a balanced pair of conductors that carry a +5 volt signal. This connector configuration can only carry messages in one direction, so a second cable is necessary for two-way communication. Some proprietary applications, such as phantom-powered footswitch controllers, use the spare pins for direct current (DC) power transmission.
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| A MIDI connector, showing the pins as numbered. |
Most devices do not copy messages from their input to their output port. A third type of port, the "thru" port, emits a copy of everything received at the input port, allowing data to be forwarded to another instrument in a "daisy chain" arrangement.Not all devices contain thru ports, and devices that lack the ability to generate MIDI data, such as effects units and sound modules, may not include out ports.
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| MIDI connectors and a MIDI cable. |
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| Two-octave MIDI controllers are popular for use with laptop computers, due to their portability. This unit provides a variety of real-time controllers, which can manipulate various sound design parameters of computer-based or standalone hardware instruments, effects, mixers and recording devices. |
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