Musical Instrument Digital Interface (; MIDI) represents an American-Japanese technical standard encompassing a communication protocol, a digital interface, and electrical connectors. This standard facilitates the interconnection of diverse electronic musical instruments, computers, and associated audio equipment for the purposes of musical performance, editing, and recording. A singular MIDI cable possesses the capacity to transmit up to sixteen distinct channels of MIDI data, each capable of being directed to an independent device. Every user interaction, whether with a key, button, knob, or slider, is transformed into a MIDI event. These events convey specific musical instructions, including a note's pitch, temporal placement, and velocity. A prevalent application of MIDI involves utilizing a MIDI keyboard or another controller to activate a digital sound module—which houses synthesized musical sounds—thereby generating audio output that is subsequently amplified for an audience. MIDI data can be transmitted through either MIDI or USB cables, or alternatively, recorded onto a sequencer or digital audio workstation for subsequent editing or playback.
Musical Instrument Digital Interface (; MIDI) is an American-Japanese technical standard that describes a communication protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, computers, and related audio devices for playing, editing, and recording music. A single MIDI cable can carry up to sixteen channels of MIDI data, each of which can be routed to a separate device. Each interaction with a key, button, knob or slider is converted into a MIDI event, which specifies musical instructions, such as a note's pitch, timing and velocity. One common MIDI application is to play a MIDI keyboard or other controller and use it to trigger a digital sound module (which contains synthesized musical sounds) to generate sounds, which the audience hears produced by a keyboard amplifier. MIDI data can be transferred via MIDI or USB cable, or recorded to a sequencer or digital audio workstation for editing or playback.
Furthermore, MIDI establishes a file format designed for the storage and exchange of this data. The advantages inherent to MIDI technology include its compact file size, the simplicity of data modification and manipulation, and the extensive array of compatible electronic instruments, as well as synthesized or digitally sampled sounds it supports. While a MIDI recording of a keyboard performance might initially emulate a piano or another keyboard instrument, the nature of MIDI—which captures messages and note information rather than specific audio waveforms—allows this recording to be reinterpreted with a multitude of alternative sounds, from synthesized or sampled guitars and flutes to an entire orchestral ensemble.
Prior to the advent of MIDI, electronic musical instruments produced by various manufacturers possessed restricted interoperability, primarily relying on CV/gate connections for communication. The introduction of MIDI revolutionized this landscape, enabling any MIDI-compatible keyboard or other controller device to seamlessly connect with any other MIDI-compatible sequencer, sound module, drum machine, synthesizer, or computer, irrespective of their respective manufacturers.
MIDI technology achieved standardization in 1983 through the collaborative efforts of a panel comprising music industry representatives. Its ongoing maintenance is overseen by the MIDI Manufacturers Association (MMA). All official MIDI standards are collaboratively developed and disseminated by the MMA, based in Los Angeles, and the MIDI Committee of the Association of Musical Electronics Industry (AMEI), located in Tokyo. In 2016, the MMA founded The MIDI Association (TMA) with the objective of fostering a global community for individuals engaged in working, performing, or creating with MIDI.
History
During the early 1980s, a significant challenge existed in the absence of a standardized method for synchronizing electronic musical instruments produced by diverse manufacturers. Each company typically employed its own proprietary synchronization standards, examples of which included CV/gate, DIN sync, and the Digital Control Bus (DCB). Ikutaro Kakehashi, then president of Roland, recognized that this lack of standardization impeded the expansion of the electronic music industry. Consequently, in June 1981, he initiated a proposal for the development of a universal standard, presenting this idea to Tom Oberheim, the founder of Oberheim Electronics, who had previously devised his own proprietary interface, the Oberheim Parallel Bus.
Kakehashi deemed Oberheim's existing system overly complex and subsequently engaged with Dave Smith, president of Sequential Circuits, to explore the creation of a more streamlined and cost-effective alternative. While Smith pursued discussions regarding this concept with American corporations, Kakehashi concurrently consulted with Japanese firms including Yamaha, Korg, and Kawai. Representatives from all these companies convened in October to deliberate the proposal. Initially, only Sequential Circuits and the aforementioned Japanese companies expressed interest.
Leveraging Roland's DCB as a foundational framework, Smith and Sequential Circuits engineer Chet Wood engineered a universal interface designed to facilitate communication among equipment from various manufacturers. Smith and Wood formally introduced this standard in a paper titled Universal Synthesizer Interface, presented at the Audio Engineering Society show in October 1981. The proposed standard underwent subsequent discussion and refinement by representatives from Roland, Yamaha, Korg, Kawai, and Sequential Circuits. Kakehashi initially advocated for the name Universal Musical Interface (UMI), pronounced you-me; however, Smith considered this appellation "a little corny." Nevertheless, Smith appreciated the substitution of instrument for synthesizer and consequently proposed the designation Musical Instrument Digital Interface (MIDI). Robert Moog, president of Moog Music, officially announced MIDI in the October 1982 edition of Keyboard.
At the 1983 Winter NAMM Show, Smith demonstrated a MIDI connection between Prophet 600 and Roland JP-6 synthesizers. The MIDI specification was subsequently published in August 1983. Kakehashi and Smith officially unveiled the MIDI standard, for which they were jointly awarded Technical Grammy Awards in 2013. That same year, the first MIDI-equipped instruments, the Roland Jupiter-6 and the Prophet 600, were released, alongside the inaugural MIDI drum machine, the Roland TR-909, and the first MIDI sequencer, the Roland MSQ-700.
The MIDI Manufacturers Association (MMA) was established following a gathering of "all interested companies" at the 1984 Summer NAMM Show in Chicago. The MIDI 1.0 Detailed Specification was subsequently released during the MMA's second meeting at the 1985 Summer NAMM Show. The standard underwent continuous evolution, incorporating standardized song files in 1991 with General MIDI and adapting to contemporary connection protocols such as USB and FireWire. In 2016, the MIDI Association was formed to maintain oversight of the standard. An abridged version of MIDI 1.0 was published as the international standard IEC 63035 in 2017. An initiative to develop a 2.0 standard was announced in January 2019, with the MIDI 2.0 standard officially introduced at the 2020 Winter NAMM Show.
The BBC recognized MIDI as an early instance of open-source technology. Smith articulated his belief that MIDI's success was contingent upon its universal adoption by manufacturers, necessitating that "we had to give it away."
Impact
Initially, MIDI's appeal was confined to professional musicians and record producers seeking to integrate electronic instruments into popular music production. The standard's capacity to enable communication between diverse instruments and computers catalyzed a rapid expansion in the sales and manufacturing of electronic instruments and music software. This interoperability allowed one device to control another, thereby reducing the amount of hardware musicians required. MIDI's emergence coincided with the advent of the personal computer era and the introduction of samplers and digital synthesizers. The innovative possibilities afforded by MIDI technology are widely credited with contributing to the revitalization of the music industry during the 1980s.
MIDI introduced transformative capabilities that fundamentally altered the working methods of many musicians. MIDI sequencing empowers users without formal notation skills to construct intricate musical arrangements. A musical ensemble comprising as few as one or two members, each operating multiple MIDI-enabled devices, can achieve a performance comparable to that of a larger group of musicians. This technology significantly reduces or eliminates the expense associated with hiring external musicians for a project, enabling complex productions to be realized on systems as compact as a synthesizer with an integrated keyboard and sequencer.
Furthermore, MIDI played a crucial role in establishing home recording practices. By conducting preproduction in a domestic setting, artists can mitigate recording costs by presenting a partially completed song at a professional studio. In 2022, the Guardian asserted that MIDI retained an importance to music analogous to USB's significance in computing, representing "a crucial value system of cooperation and mutual benefit, one all but thrown out by today's major tech companies in favour of captive markets." In 2005, Smith's MIDI Specification was inducted into the TECnology Hall of Fame, an accolade bestowed upon "products and innovations that have had an enduring impact on the development of audio technology." As of 2022, Smith's original MIDI design continues to be actively utilized.
Applications
Instrument control
MIDI was conceived to facilitate communication among electronic or digital musical instruments, enabling one instrument to control another. For instance, a MIDI-compatible sequencer can trigger rhythmic patterns generated by a drum sound module. Analog synthesizers, lacking digital components and predating MIDI's development, can be retrofitted with kits that convert MIDI messages into analog control voltages. When a note is played on a MIDI instrument, it generates a digital MIDI message capable of triggering a corresponding note on a different instrument. This remote control capability allows smaller sound modules to substitute for full-sized instruments, and musicians can combine instruments to achieve a richer sound or blend distinct instrument timbres, such as acoustic piano and strings. MIDI also extends remote control to various instrument parameters, including volume and effects.
Synthesizers and samplers incorporate diverse functionalities for manipulating electronic or digital audio. Filters modify timbre, while envelopes regulate the temporal evolution of a sound following note activation. Synthesizer parameters, such as filter frequency and envelope attack (the duration required for a sound to attain its peak amplitude), are amenable to remote control via MIDI. Effect units possess distinct parameters, including delay feedback and reverb time. When a MIDI continuous controller number (CCN) is allocated to a specific parameter, the device processes incoming messages associated with that identifier. These messages can be transmitted using various controls, such as knobs, switches, and pedals. A configured set of parameters can be stored in a device's internal memory as a patch, which can then be remotely recalled through MIDI program changes.
Musical Composition
MIDI events are amenable to sequencing using either computer software or dedicated hardware music workstations. Numerous digital audio workstations (DAWs) are engineered with MIDI as a fundamental, integrated element. The integration of MIDI piano rolls within many DAWs facilitates the straightforward modification of recorded MIDI messages. Such functionalities empower composers to review and refine their creations with significantly greater speed and efficacy compared to traditional methods like multitrack recording. Furthermore, MIDI enables the programming of compositions that transcend the capabilities of human performers.
Given that a MIDI performance constitutes a series of commands generating sound, MIDI recordings offer manipulation possibilities unavailable to audio recordings. This includes the capacity to alter the key, instrumentation, or tempo of a MIDI arrangement, rearrange its constituent sections, or even modify individual notes. The facility to conceptualize musical ideas and promptly hear their playback fosters extensive experimentation among composers.
Algorithmic composition software generates computer-produced performances, which can serve as foundational musical concepts or accompaniment.
Certain composers leverage the standardized and portable command and parameter sets within MIDI 1.0 and General MIDI (GM) for inter-instrument musical data exchange. Data generated through sequenced MIDI recordings can be stored as a standard MIDI file (SMF), enabling digital dissemination and reproduction across any computer or electronic instrument compliant with MIDI, GM, and SMF standards. Notably, MIDI data files are considerably more compact than their equivalent recorded audio counterparts.
Integration with Computing Systems
The emergence of MIDI coincided with the stabilization of the personal computer market, positioning computers as a feasible platform for music production. By 1983, computers began to significantly influence mainstream music production. Following the 1983 ratification of the MIDI specification, MIDI functionalities were subsequently integrated into various nascent computer architectures. For instance, the Yamaha CX5M, released in 1984, incorporated MIDI support and sequencing capabilities within an MSX system.
The proliferation of MIDI on home computing platforms was substantially advanced by the Roland Corporation's MPU-401, introduced in 1984. This device was notable as the inaugural MIDI-equipped sound card, offering both MIDI sound processing and sequencing functionalities. Roland's subsequent distribution of MPU sound chips to other sound card manufacturers established a de facto universal MIDI-to-PC interface standard. The broad acceptance of MIDI spurred the development of computer-centric MIDI software. Shortly thereafter, numerous computing platforms, including the Apple II, Macintosh, Commodore 64, Amiga, Acorn Archimedes, and IBM PC compatibles, began to support MIDI. Notably, the 1985 Atari ST was released with integrated MIDI ports as a standard feature.
In 2015, Retro Innovations introduced the initial MIDI interface for the VIC-20, thereby enabling electronic musicians and retro-computing aficionados to access the computer's four voices. Retro Innovations additionally produces MIDI interface cartridges compatible with Tandy Color Computer and Dragon computers.
Chiptune artists utilize vintage gaming consoles for musical composition, production, and performance, facilitated by MIDI interfaces. Specialized interfaces are procurable for platforms such as the Family Computer/Nintendo Entertainment System, Game Boy, Game Boy Advance, and Sega Mega Drive/Sega Genesis.
Computer File Management
MIDI files do not constitute audio recordings. Instead, they comprise a series of instructions, such as those for pitch or tempo, and typically occupy significantly less disk space—potentially a thousandfold reduction—compared to an equivalent audio recording. The minimal file size of MIDI arrangements made them an appealing method for online music sharing prior to the widespread availability of broadband internet and multi-gigabyte storage devices. A significant limitation, however, stemmed from the considerable variability in the quality of users' audio cards and the actual audio content (samples or synthesized sounds) within these cards, to which MIDI data merely refers symbolically. Even high-quality sound cards featuring sampled sounds could exhibit inconsistent fidelity across different sampled instruments. Initial cost-effective sound cards, including the AdLib, Sound Blaster, and their compatible counterparts, employed a simplified iteration of Yamaha's frequency modulation synthesis (FM synthesis) technology, rendered via low-quality digital-to-analog converters. The resulting low-fidelity output from these prevalent cards was frequently, though erroneously, attributed to MIDI technology itself. This misconception fostered a perception of MIDI as inherently low-quality audio, despite MIDI containing no actual sound; its playback fidelity is solely determined by the capabilities of the sound-generating hardware.
The Standard MIDI File (SMF) format offers a standardized methodology for storing, transferring, and accessing musical sequences across various systems. This standard was developed and is continuously managed by the MMA, typically utilizing a .mid file extension. Their diminutive size facilitated extensive adoption in computing, mobile phone ringtones, web page development, and musical greeting cards. Designed for broad compatibility, these files encapsulate data such as note values, temporal information, and track identifiers. Lyrics can be embedded as metadata, enabling their display by karaoke devices.
Standard MIDI Files (SMFs) are generated as an export format from software sequencers or hardware workstations. These files structure MIDI messages into one or more parallel tracks, timestamping events to ensure sequential playback. A header section specifies the arrangement's track count, tempo, and designates which of the three SMF formats the file employs. A Type 0 file consolidates the complete performance onto a single track, whereas Type 1 files can accommodate multiple synchronously performed tracks. Type 2 files are infrequently utilized and serve to store several distinct arrangements, each with its own track intended for sequential playback.
RMID Files
Microsoft Windows integrates Standard MIDI Files (SMFs) with Downloadable Sounds (DLS) within a Resource Interchange File Format (RIFF) wrapper, designated as RMID files and bearing a .rmi extension. The RIFF-RMID format has since been superseded by Extensible Music Files (XMF).
Software
A primary benefit of incorporating a personal computer into a MIDI system is its versatility, enabling it to fulfill diverse functions based on the installed software. Multitasking capabilities facilitate the concurrent execution of multiple applications, potentially allowing for inter-program data exchange.
Sequencers
Sequencing software provides functionalities for manipulating recorded MIDI data through conventional computer editing operations, including cut, copy, paste, and drag-and-drop. Keyboard shortcuts enhance workflow efficiency, and in certain configurations, editing functions can be triggered by MIDI events. The sequencer allows for assigning distinct sounds to individual channels and presents a graphical representation of the musical arrangement. A comprehensive suite of editing tools is accessible, encompassing a notation display or scorewriter for generating printable musical parts for performers. Features like looping, quantization, randomization, and transposition streamline the arrangement workflow.
The process of beat creation is simplified, and groove templates can be employed to replicate the rhythmic characteristics of other tracks. Enhanced realism in musical expression can be achieved by manipulating real-time controllers. Mixing operations are feasible, and MIDI data can be synchronized with recorded audio and video tracks. Projects can be saved and transferred across various computing environments or studios.
Sequencers can manifest in alternative configurations, including drum pattern editors that enable users to construct beats via grid-based input, and loop sequencers like ACID Pro, which integrate MIDI with pre-recorded audio loops whose tempos and keys are automatically aligned. Cue-list sequencing is employed to initiate dialogue, sound effects, and musical cues within stage and broadcast productions.
Notation Software
MIDI technology enables the automatic transcription of keyboard performances into sheet music. Scorewriting software, generally lacking sophisticated sequencing capabilities, is primarily designed to produce clean, professional printouts for live musicians. Such applications offer features like dynamics and expression markings, chord and lyric presentation, and diverse score formatting options. Additionally, specialized software exists for generating braille scores.
Prominent notation software packages encompass Finale, Encore, Sibelius, MuseScore, and Dorico. Furthermore, SmartScore software facilitates the generation of MIDI files from scanned sheet music.
Editors and Librarians
Patch editors serve as computer interfaces, allowing users to program their equipment. These tools became indispensable with the advent of intricate synthesizers, such as the Yamaha FS1R, which featured thousands of programmable parameters but possessed a minimalist interface comprising fifteen small buttons, four knobs, and a compact LCD. While digital instruments often deter user experimentation due to their limited tactile feedback and direct control compared to physical switches and knobs, patch editors provide hardware instrument and effects device owners with the same comprehensive editing capabilities available to software synthesizer users. Some editors are tailored for specific instruments or effects units, whereas other, universal editors accommodate a diverse range of equipment, ideally enabling control over all device parameters within a setup via System Exclusive messages. System Exclusive messages leverage the MIDI protocol to transmit data concerning a synthesizer's parameters.
Patch librarians fulfill the specialized role of organizing sound collections across various equipment and facilitating the transfer of complete sound banks between an instrument and a computer. This mechanism effectively expands a device's restricted patch storage by utilizing a computer's significantly larger disk capacity. Once transferred to a computer, customized patches can be distributed among other owners of the identical instrument. Historically, universal editor/librarians, which integrated both functions, were prevalent, exemplified by Opcode Systems' Galaxy, eMagic's SoundDiver, and MOTU's Unisyn. Despite the widespread abandonment of these legacy programs due to the shift towards computer-based synthesis with virtual instruments, several contemporary editor/librarians persist, including Coffeeshopped Patch Base, Sound Quest's Midi Quest, and various offerings from Sound Tower. Native Instruments' Kore represented an attempt to adapt the editor/librarian paradigm for software instruments but was discontinued in 2011.
Auto-Accompaniment Programs
Software applications capable of dynamically generating accompaniment tracks are designated as auto-accompaniment programs. These applications construct full-band arrangements based on user-selected styles and transmit the output to a MIDI sound-generating device for reproduction. The resulting tracks serve various purposes, including educational or practice aids, live performance accompaniment, or songwriting assistance.
Synthesis and Sampling
Computers can employ software to produce audio, which subsequently passes through a digital-to-analog converter (DAC) to a power amplifier and loudspeaker system. The simultaneous playback capacity (polyphony) is contingent upon the computer's CPU performance, as are the sample rate and bit depth of playback, both of which directly influence sound fidelity. Software-based synthesizers are susceptible to timing discrepancies not typically encountered with hardware instruments, whose dedicated operating systems are immune to interruptions from background processes common in desktop environments. Such timing issues can lead to synchronization problems and audible artifacts like clicks and pops during interrupted sample playback. Furthermore, software synthesizers may introduce additional latency in their sound generation.
The origins of software synthesis trace back to the 1950s, when Max Mathews at Bell Labs developed the MUSIC-N programming language, enabling non-real-time sound generation. An early synthesizer, Reality, developed by Dave Smith's Seer Systems, operated directly on a host computer's central processing unit (CPU). This system achieved minimal latency via close driver integration, consequently limiting its compatibility to Creative Labs soundcards. Syntauri Corporation's Alpha Syntauri represented another pioneering software-driven synthesizer. Operating on the Apple IIe computer, it utilized a hybrid approach of software and hardware to generate additive synthesis. Certain systems incorporate dedicated hardware to mitigate the processing burden on the host CPU, exemplified by Symbolic Sound Corporation's Kyma System and the Creamware/Sonic Core Pulsar/SCOPE systems, which collectively power a comprehensive suite of recording studio instruments, effect units, and mixers. The capability to construct complete MIDI arrangements exclusively within computer software empowers composers to render a final output directly as an audio file.
Music in Gaming
Before the mid-1990s, floppy disks served as the predominant distribution medium for games compatible with IBM PCs. The compact nature of MIDI files rendered them a practical method for delivering game soundtracks. Before the advent of Windows 95, games commonly utilized either Ad Lib or Sound Blaster audio cards. These cards employed FM synthesis, a technique that produces sound by modulating sine waves. John Chowning, the innovator of this technique, posited that the technology could precisely replicate any sound given a sufficient number of sine waves; however, most computer audio cards implemented FM synthesis using only two sine waves. This limitation, coupled with the cards' 8-bit audio capabilities, produced a sound quality often characterized as "artificial" and "primitive".
Subsequently, wavetable daughterboards became available, offering audio samples as an alternative to FM synthesis. While costly, these boards frequently incorporated sounds derived from highly regarded MIDI instruments, such as the E-mu Proteus. By the mid-1990s, the computer industry transitioned to wavetable-based soundcards featuring 16-bit playback; however, a standardized 2 MB of wavetable storage proved insufficient for accommodating high-quality samples of 128 General MIDI instruments and associated drum kits. To optimize the constrained storage capacity, certain manufacturers stored 12-bit samples, which were then expanded to 16 bits during playback.
Diverse Applications
Notwithstanding its primary association with musical instruments, MIDI is capable of controlling any electronic or digital device equipped to interpret and process MIDI commands. Consequently, MIDI has been adopted as a control protocol across various non-musical domains. For instance, MIDI Show Control employs MIDI commands to manage stage lighting systems and initiate synchronized events in theatrical productions. Visual jockeys (VJs) and turntablists utilize MIDI for cueing clips and synchronizing equipment, while recording systems leverage it for synchronization and automation. Wayne Lytle, the founder of Animusic, developed a system named MIDIMotion, which he employed to create the Animusic series of computer-animated music video albums. Animusic subsequently developed proprietary animation software, Animotion, specifically tailored for MIDIMotion. Apple Motion also facilitates comparable control over animation parameters via MIDI. Furthermore, the 1987 first-person shooter game MIDI Maze and the 1990 Atari ST puzzle video game Oxyd both utilized MIDI for computer networking.
MIDI Devices
Connectivity and Interface Standards
DIN Connector Specification
According to the original MIDI 1.0 standard, cables are terminated with a 180° five-pin DIN connector (DIN 41524). Standard implementations utilize only three of the five conductors: a ground wire (pin 2) and a balanced pair of conductors (pins 4 and 5) responsible for transmitting the MIDI signal as an electrical current. This specific connector configuration supports unidirectional message transmission, necessitating a second cable for bidirectional communication. Certain proprietary applications, such as phantom-powered footswitch controllers, employ the unused pins for direct current (DC) power transmission.
Opto-isolators maintain electrical isolation between MIDI devices and their connections, thereby preventing ground loops and safeguarding equipment against voltage spikes. Given the absence of error detection capabilities within MIDI, the maximum recommended cable length is restricted to 15 meters (49 ft) to mitigate potential interference.
TRS Minijack Connector Standard
For space optimization, certain MIDI devices, particularly compact models, adopted the use of 3.5 mm TRS phone connectors, also known as audio minijack connectors. Its widespread adoption prompted the MIDI Manufacturers' Association to standardize its wiring configuration. The MIDI-over-minijack standards document further advocates for the utilization of 2.5 mm connectors over 3.5 mm ones to mitigate potential ambiguity with audio interfaces.
Thru port
Typically, MIDI devices do not replicate incoming messages to their output ports. Conversely, a distinct port type, designated as the thru port, duplicates all data received at the input, facilitating the transmission of information to subsequent instruments within a daisy-chain configuration. The inclusion of thru ports is not universal across all devices; furthermore, units incapable of generating MIDI data, such as effects processors and sound modules, may omit output ports entirely.
Management devices
Sequential connection of MIDI devices in a daisy chain introduces cumulative signal latency. This latency can be mitigated through the deployment of a MIDI thru box, which features multiple outputs, each delivering an identical replication of the input signal. A MIDI merger consolidates input from several devices into a unified data stream, thereby enabling the connection of multiple controllers to a singular target device. MIDI switchers facilitate selection among various devices, obviating the need for manual cable reconfigurations. MIDI routers integrate these functionalities, offering multiple inputs and outputs capable of directing any combination of input channels to any desired output configuration. Configuration of routing schemes can be accomplished via computer software, subsequently stored in internal memory, and recalled using MIDI program change commands. Consequently, these devices can operate as autonomous MIDI routers in environments lacking a host computer. MIDI data processors serve various utility functions and facilitate specialized effects. Examples encompass MIDI filters, which expunge extraneous MIDI data from the stream, and MIDI delays, which generate timed repetitions of the input data.
Interfaces
The primary role of a computer MIDI interface is to establish synchronized communication between a MIDI device and a host computer. While certain computer sound cards incorporate a standard MIDI connector, alternative connection methods include the D-subminiature DA-15 game port, USB, FireWire, Ethernet, or proprietary interfaces. The proliferation of USB connectors during the 2000s facilitated the widespread availability of MIDI-to-USB data interfaces, enabling the transmission of MIDI channels to computers equipped with USB ports. Certain MIDI keyboard controllers feature integrated USB ports, allowing direct connectivity to computers running music production software.
The serial nature of MIDI transmission inherently introduces timing discrepancies. A standard three-byte MIDI message necessitates approximately one millisecond for complete transmission. Given its serial architecture, MIDI can process only a single event concurrently. Consequently, if an event is simultaneously directed to two channels, the transmission for the second channel will be deferred until the first is complete, resulting in a one-millisecond delay. When an event is broadcast across all available channels simultaneously, the final channel's transmission may experience a delay of up to sixteen milliseconds. This inherent latency spurred the development of MIDI interfaces featuring multiple input and output ports, as distributing events across distinct ports enhances timing precision compared to routing multiple channels through a single port. The phenomenon of audible timing inaccuracies arising from delayed MIDI transmission is commonly termed MIDI slop.
Controllers
MIDI controllers are broadly categorized into two types: performance controllers, which generate musical notes for performance, and utility controllers, which transmit various real-time events without necessarily producing notes. Numerous devices integrate functionalities from both controller categories.
Keyboards represent the predominant category of MIDI controllers. Given that MIDI's initial design prioritized keyboard interfaces, any non-keyboard controller is categorized as an "alternative." While this design focus was initially perceived as a constraint by composers disinclined towards keyboard-centric music, the standard demonstrated sufficient flexibility. Consequently, MIDI compatibility was extended to diverse controller types, encompassing guitars, other stringed instruments, drum controllers, wind controllers (which simulate drum kit and wind instrument performance, respectively), and various specialized or experimental devices. Nonetheless, certain aspects of keyboard performance, central to MIDI's original conception, do not comprehensively accommodate the expressive potential of other instruments. Jaron Lanier, for instance, identifies the standard as an instance of technological "lock-in," inadvertently restricting the scope of musical expression. Subsequent extensions to the protocol have sought to mitigate some of these identified deficiencies.
While software synthesizers offer substantial power and versatility, some musicians contend that the cognitive load associated with managing both a MIDI keyboard and a computer interface (keyboard and mouse) diminishes the immediacy of the performance experience. In contrast, dedicated hardware devices for real-time MIDI control offer ergonomic advantages and can foster a more profound connection with the instrument compared to computer-based interfaces. These controllers can be either general-purpose, designed for broad compatibility across various equipment, or application-specific, tailored to operate with particular software. Illustrative examples of the latter include Akai's APC40 controller, optimized for Ableton Live, and Korg's MS-20ic controller, which replicates the control panel of their MS-20 analog synthesizer. The MS-20ic controller notably incorporates patch cables, enabling signal routing control within its virtual MS-20 synthesizer reproduction, and also facilitates the control of external, third-party devices.
Instruments
A typical MIDI instrument comprises several essential components: ports for transmitting and receiving MIDI signals, a central processing unit (CPU) for signal processing, a user interface for programming, audio circuitry responsible for sound generation, and various controllers. The instrument's operating system and its default factory sounds are frequently stored within a read-only memory (ROM) unit.
Alternatively, a MIDI instrument may manifest as a stand-alone module, devoid of a piano-style keyboard. Such modules typically integrate a General MIDI soundboard (supporting GM, GS, and XG standards) and offer onboard editing functionalities, encompassing transposition, MIDI instrument selection, and adjustments for volume, pan, reverb levels, and other MIDI controller parameters. These MIDI modules commonly feature a display screen, enabling users to monitor information pertinent to the currently active function.
Synthesizers
Synthesizers utilize a diverse array of sound generation techniques. They can be configured with an integrated keyboard or exist as dedicated sound modules that produce audio when activated by an external controller, such as a MIDI keyboard. Sound modules are frequently engineered for installation within a standard 19-inch rack system. Manufacturers commonly offer synthesizers in both standalone and rack-mounted configurations, with keyboard-equipped versions often available in multiple size variations.
Samplers
A sampler is an instrument capable of recording and digitizing audio, storing it in random-access memory (RAM), and subsequently playing it back. Users typically have the ability to edit a recorded sample, save it to a hard disk, apply various effects, and sculpt its characteristics using techniques analogous to those employed by subtractive synthesizers. Samplers are also available in both keyboard-integrated and rack-mounted configurations. Instruments that generate sounds exclusively through sample playback, lacking any recording functionality, are designated as "ROMplers."
The widespread adoption of samplers as viable MIDI instruments lagged behind that of synthesizers, primarily attributable to the high cost of memory and processing power during their early development. The Ensoniq Mirage, introduced in 1984, marked the advent of the first low-cost MIDI sampler. A common limitation of MIDI samplers is their typically small integrated displays, which hinder effective editing of sampled waveforms, although some models offer connectivity to external computer monitors for enhanced visual interface.
Drum machines
Drum machines are characteristically sample playback devices specifically designed for the reproduction of drum and percussion sounds. They commonly incorporate an integrated sequencer, facilitating the creation of drum patterns and their arrangement into complete musical compositions. Multiple audio outputs are frequently provided, enabling the routing of individual sounds or sound groups to distinct outputs. Furthermore, the discrete drum voices within a drum machine can often be triggered and played from an external MIDI instrument or a dedicated sequencer.
Workstations and hardware sequencers
Sequencer technology existed prior to the advent of MIDI. Analog sequencers employ CV/Gate signals for the control of pre-MIDI analog synthesizers. MIDI sequencers commonly feature transport controls analogous to those found on tape recorders. They are designed to record MIDI performances and organize them into distinct tracks, adhering to a multitrack recording methodology. Music workstations integrate controller keyboards, an internal sound generator, and a sequencer. Such workstations facilitate the creation of comprehensive musical arrangements, enabling playback via their integrated sound capabilities, thereby functioning as autonomous music production environments. Furthermore, they typically incorporate functionalities for file storage and transfer.
Effects Processors
Certain effects processors offer remote control capabilities through MIDI. For instance, the Eventide H3000 Ultra-harmonizer provides such comprehensive MIDI control that it can effectively be utilized as a synthesizer. Similarly, the Drum Buddy, a drum machine designed in a pedal format, incorporates a MIDI connection, enabling its tempo to be synchronized with devices such as looper pedals or time-based effects like delay units.
Technical Specifications
MIDI messages comprise 8-bit bytes, which are transmitted at a rate of 31,250 (±1%) baud via 8-N-1 asynchronous serial communication, as illustrated in the accompanying figure. The initial bit of each byte serves to classify it as either a status byte or a data byte, with the subsequent seven bits conveying the informational content.
A MIDI connection is capable of transmitting data across sixteen distinct channels, designated from 1 to 16. A receiving device can be configured to process messages exclusively from designated channels while disregarding others (referred to as omni off mode), or it can monitor all channels, thereby effectively bypassing the channel address (known as omni on mode).
A polyphonic device possesses the capacity to generate multiple notes concurrently, continuing until its polyphony threshold is met, the notes complete their decay envelope, or explicit note-off MIDI commands are received. Conversely, a monophonic device will cease any currently sounding note upon the reception of new note-on commands.
Some receiving devices offer the flexibility to be configured in all four permutations of omni off/on and mono/poly modes.
MIDI Messages
A MIDI message constitutes an instruction designed to govern a particular function of the receiving device. Each MIDI message is composed of a status byte, which specifies the message type, succeeded by a maximum of two data bytes that encapsulate the relevant parameters. MIDI messages are categorized as either channel messages, which are transmitted on a single designated channel and processed exclusively by devices assigned to that channel, or as system messages, which are universally received by all connected devices. Individual receiving devices disregard any data that is not pertinent to their specific operational capabilities. The five primary message classifications include Channel Voice, Channel Mode, System Common, System Real-Time, and System Exclusive.
Channel Voice messages are designed to convey real-time performance data across a singular channel. Illustrative examples encompass note-on messages, which encapsulate a MIDI note number defining the pitch, a velocity value signifying the intensity of the note's articulation, and the associated channel number; note-off messages, which terminate a sounding note; program change messages, which alter a device's patch; and control change messages, which facilitate the modification of an instrument's various parameters. MIDI notes are numerically indexed from 0 to 127, corresponding to pitches from C−1 to G9, with middle C§89§ assigned note number 60. This range surpasses the standard 88-note piano's span from A§1011§ to C§1213§, encompassing a frequency spectrum from 8.175799 Hz to 12543.85 Hz.
System Exclusive Messages
System Exclusive (SysEx) messages are utilized to transmit data pertaining to a synthesizer's operational functions, as distinct from performance-oriented information like note values or loudness. Their capacity to incorporate functionalities extending beyond the provisions of the core MIDI standard significantly contributes to the protocol's adaptability and enduring relevance. Manufacturers leverage these messages to develop proprietary commands, enabling more comprehensive control over their equipment than is achievable through the constraints of standard MIDI messages.
The MIDI Manufacturers Association assigns a distinct identification number to each MIDI-compliant company. These identifiers are embedded within SysEx messages, guaranteeing that only the intended recipient device processes the message, while all other devices are programmed to disregard it. Furthermore, numerous instruments incorporate a SysEx ID configuration, which permits a single controller to address two devices of identical models autonomously.
Universal System Exclusive messages represent a distinct category of SysEx messages, designed for MIDI extensions that are not proprietary to a single manufacturer.
Implementation Chart
MIDI devices generally do not support every message type outlined in the MIDI specification. To address this, the MIDI implementation chart was standardized by the MMA, providing users with a clear overview of an instrument's specific capabilities and its message response behavior. This chart is typically included in the documentation accompanying MIDI devices.
Electrical Specifications
The electrical interface for MIDI 1.0 is structured around a fully isolated current loop, as depicted by the red and blue lines in the subsequent schematic:
Within this schematic, the designation "DIN / TRS" signifies the permissible use of either a DIN connector or a TRS phone connector.
For the transmission of a logic 0 and a start bit, the sender's UART generates a low voltage. This action initiates a nominal 5-milliampere current flow, originating from the sender's high-voltage supply. This current propagates rightward along the red lines through the shielded twisted-pair cable, entering the receiver's opto-isolator. Subsequently, the current exits the opto-isolator and returns leftward along the blue lines to the sender's UART, which then sinks the current. Resistors R1 and R2 are configured to limit the current and are matched to ensure balanced impedance. A diode is incorporated for protective purposes. This current activates the opto-isolator's LED and phototransistor, enabling the receiver's UART to interpret the signal, facilitated by pull-up resistor R3 connected to the receiver's voltage supply. Although the original specification mandates 5-volt supplies, both the receiver and sender are capable of operating with differing voltage levels.
Conversely, for the transmission of a logic 1, a stop bit, or during idle states, the sender's UART maintains a high voltage equivalent to its power supply, thereby preventing any current flow. This design choice effectively conserves power during periods of inactivity.
Extensions
The inherent flexibility and pervasive adoption of MIDI have facilitated numerous refinements to its standard, thereby extending its applicability to functions beyond its initial design scope.
General MIDI
While MIDI facilitates the selection of instrument sounds via program change messages, it does not guarantee consistent sound assignments across different instruments for a given program location. For instance, Program #0 might correspond to a piano on one device and a flute on another. To address this variability, the General MIDI (GM) standard was introduced in 1991. GM establishes a standardized sound bank, ensuring that a Standard MIDI File created on one device will produce a similar auditory experience when played back on another. The GM specification defines a bank of 128 sounds, organized into 16 families, each containing eight related instruments, with a unique program number assigned to each instrument. Consequently, a specific program change command will consistently select the identical instrument sound on any GM-compatible device. Furthermore, percussion instruments are allocated to channel 10, with each percussion sound mapped to a distinct MIDI note value.
The GM standard also resolves inconsistencies in note mapping. Prior to GM, manufacturers held differing views on the MIDI note number corresponding to middle C. GM definitively specifies that note number 69 produces A440, thereby establishing middle C as note number 60.
Devices adhering to the GM standard are required to provide 24-note polyphony. Furthermore, GM-compatible instruments must respond to velocity, aftertouch, and pitch bend, with these parameters set to predefined default values upon startup. Support for specific controller numbers, such as those for the sustain pedal, and Registered Parameter Numbers (RPNs) is also mandatory.
A streamlined iteration of GM, designated as GM Lite, is employed for devices possessing constrained processing capabilities.
GS, XG, and GM2
A consensus rapidly emerged that the 128-instrument sound set provided by General MIDI was insufficient. In response, Roland introduced its General Standard (GS), which incorporated supplementary sounds, drum kits, and effects. GS also provided a bank select command for accessing these additions and utilized MIDI Non-Registered Parameter Numbers (NRPNs) to control its new functionalities. Yamaha subsequently launched its Extended General MIDI (XG) in 1994. XG similarly expanded upon GM by offering additional sounds, drum kits, and effects, but it employed standard controllers for editing rather than NRPNs and increased polyphony to 32 voices. While both GS and XG maintain backward compatibility with the original GM specification, they are not mutually compatible. Although neither standard achieved widespread adoption beyond its respective creator, both are frequently supported by various music software applications.
The General MIDI Level 2 (GM2) specification was developed in 1999 by member companies of Japan's AMEI. GM2 retains backward compatibility with General MIDI (GM) while enhancing its capabilities, including an increased polyphony of 32 voices, standardized controller numbers for functions like sostenuto and the soft pedal (una corda), the integration of Registered Parameter Numbers (RPNs) and Universal System Exclusive Messages, and the incorporation of the MIDI Tuning Standard. Furthermore, GM2 serves as the foundational instrument selection mechanism within Scalable Polyphony MIDI (SP-MIDI), a specialized MIDI iteration designed for low-power devices, enabling dynamic adjustment of polyphony based on the device's processing capacity.
The MIDI Tuning Standard
While most MIDI synthesizers typically employ equal temperament tuning, the MIDI Tuning Standard (MTS), formally ratified in 1992, provides support for alternative tuning systems. MTS facilitates microtunings, which can be loaded from a bank containing up to 128 distinct patches, and enables real-time manipulation of note pitches. However, adherence to this standard is not mandatory for manufacturers, and even those who adopt it are not obligated to implement its full suite of features.
MIDI Time Code
Although a single sequencer can operate a MIDI system using its internal clock, multi-sequencer configurations necessitate synchronization to a unified timing source. MIDI Timecode (MTC), an innovation by Digidesign, addresses this requirement by utilizing System Exclusive (SysEx) messages specifically designed for timing synchronization. MTC is capable of bidirectional translation with the SMPTE timecode standard, and specialized MIDI interfaces, such as Mark of the Unicorn's MIDI Timepiece, can facilitate this conversion from SMPTE to MTC. A key distinction is that MIDI clock operates on tempo, whereas timecode is frame-based and thus tempo-independent. Similar to SMPTE timecode, MTC incorporates positional data and possesses the ability to recover from signal interruptions or dropouts.
MIDI Machine Control
MIDI Machine Control (MMC) comprises a collection of System Exclusive (SysEx) commands designed to manage the transport functions of hardware recording equipment. Through MMC, a sequencer can transmit commands such as Start, Stop, and Record to an attached tape deck or hard disk recording system. It also enables fast-forwarding or rewinding the device to initiate playback concurrently with the sequencer. It is important to note that MMC itself does not involve synchronization data, though the connected devices may achieve synchronization via MIDI Timecode (MTC).
MIDI Show Control
MIDI Show Control (MSC) represents a suite of System Exclusive (SysEx) commands specifically developed for sequencing and remote cueing of various show control apparatuses. These devices encompass lighting systems, music and sound playback units, and motion control mechanisms. MSC finds extensive application in diverse environments, including theatrical stage productions, museum exhibits, professional recording studio control systems, and amusement park attractions.
MIDI Timestamping
A method for mitigating MIDI timing inaccuracies involves timestamping MIDI events with their intended playback times, transmitting them in advance, and buffering them within the receiving device. This pre-transmission of data minimizes the potential for a complex musical passage to overload the communication channel. Upon storage in the receiver, the timestamped information becomes immune to timing discrepancies inherent in MIDI or USB interfaces, enabling highly accurate playback. However, the functionality of MIDI timestamping is contingent upon support from both the hardware and software components of a system. Historically, early implementations, such as MOTU's MTS, eMagic's AMT, and Steinberg's Midex 8, were mutually incompatible, necessitating that users acquire both software and hardware from the same vendor for proper operation. Presently, timestamping capabilities are integrated into FireWire MIDI interfaces, Mac OS X Core Audio, and the Linux ALSA Sequencer.
The MIDI Sample Dump Standard
An unanticipated application of System Exclusive (SysEx) messages emerged in their capacity to facilitate the transfer of audio samples between musical instruments. This discovery prompted the creation of the Sample Dump Standard (SDS), which defined a novel SysEx format specifically for sample transmission. Subsequently, SDS was enhanced through the addition of two commands, enabling the conveyance of sample loop point data without the necessity of transmitting the complete audio sample.
Downloadable Sounds
The Downloadable Sounds (DLS) specification, formally ratified in 1997, provides a mechanism for mobile devices and computer sound cards to augment their wavetables using downloadable sound sets. The subsequent DLS Level 2 specification, introduced in 2006, further established a standardized synthesizer architecture. The Mobile DLS standard integrates DLS banks with Scalable Polyphony MIDI (SP-MIDI) into self-contained Mobile XMF files.
MIDI Polyphonic Expression
MIDI Polyphonic Expression (MPE) constitutes a methodology enabling musicians to continuously manipulate pitch bend and various other expressive parameters for discrete notes. This functionality is achieved by allocating a dedicated MIDI channel to each note, thereby facilitating the individual application of controller messages. The official specifications for MPE were formally published by AMEI in November 2017 and subsequently by the MMA in January 2018. Notable instruments, including the Continuum Fingerboard, LinnStrument, ROLI Seaboard, Sensel Morph, and Eigenharp, empower users to precisely control pitch, timbre, and other subtle nuances for individual notes within chordal structures.
Alternative Hardware Transport Mechanisms
Beyond the conventional 31.25 kbit/s current-loop transmission via a DIN connector, identical data can be conveyed through diverse hardware transport protocols, including USB, FireWire, and Ethernet.
USB and FireWire Interfaces
In 1999, the USB-IF consortium established a standardized protocol for MIDI transmission over USB, formally designated as the "Universal Serial Bus Device Class Definition for MIDI Devices". The adoption of MIDI over USB has proliferated significantly, largely due to the obsolescence of prior MIDI connection interfaces, such as ISA cards and game ports, in contemporary personal computing systems. Major operating systems, including Linux, Microsoft Windows, Macintosh OS X, and Apple iOS, incorporate native class drivers to ensure compatibility with devices adhering to the "Universal Serial Bus Device Class Definition for MIDI Devices" standard.
Apple Computer pioneered the development of the FireWire interface throughout the 1990s. This technology first appeared in digital video (DV) cameras towards the close of that decade, subsequently integrating into G3 Macintosh models by 1999. Its design was specifically optimized for multimedia applications. Distinguishing itself from USB, FireWire employs intelligent controllers capable of autonomous data transmission management, thereby alleviating processing demands on the central processing unit (CPU). Furthermore, akin to conventional MIDI devices, FireWire-enabled instruments can establish direct communication without requiring an intermediary computer.
XLR Connectors
The Octave-Plateau Voyetra-8 synthesizer represented an early instance of MIDI integration, uniquely employing XLR3 connectors instead of the standard 5-pin DIN. Initially launched prior to the widespread adoption of MIDI, this instrument was subsequently upgraded with a MIDI interface while retaining its original XLR connector configuration.
Serial, Parallel, and Joystick Ports
With the increasing prevalence of computer-centric studio environments, MIDI devices capable of direct computer connectivity emerged. These devices commonly utilized the 8-pin mini-DIN connector, which Apple had previously employed for serial ports before the release of the Blue and White G3 models. Advanced MIDI interfaces, exemplified by the Mark of the Unicorn MIDI Time Piece, designed as central studio components, leveraged a high-speed transmission mode that exploited the serial ports' capacity to operate at twenty times the conventional MIDI data rate. Towards the late 1990s, certain MIDI instruments incorporated integrated mini-DIN ports for direct computer interfacing. Additionally, some peripherals established connections via a PC's DB-25 parallel port or through the DA-15 game port, frequently present on many PC sound cards.
mLAN Protocol
Yamaha launched the mLAN protocol in 1999. This system was conceptualized as a local area network specifically for musical instruments, employing FireWire as its underlying transport mechanism. Its design facilitated the simultaneous transmission of multiple MIDI channels, multichannel digital audio, data file transfers, and timecode information. mLAN found application in various Yamaha products, particularly digital mixing consoles and the Motif synthesizer, as well as in third-party offerings like the PreSonus FIREstation and the Korg Triton Studio. However, no new mLAN-compatible products have been introduced since 2007.
SCSI MIDI Device Interface (SMDI)
During the 1990s, the SCSI MIDI Device Interface (SMDI) was adopted by certain samplers and hard disk recorders, including the Kurzweil K2000 and Peavey SP Sample Playback Synthesizer. This interface enabled rapid bidirectional sample transfer to both hard disk drives and magneto-optical drives.
Ethernet and Internet Protocol Implementations
Network-based implementations of MIDI offer advanced routing functionalities and the high-bandwidth communication channels that prior MIDI alternatives, such as ZIPI, aimed to provide. Proprietary systems have been in existence since the 1980s, with some utilizing fiber optic cables for data transmission. The RTP-MIDI open specification, developed by the Internet Engineering Task Force, has garnered significant industry endorsement. Apple has integrated support for this protocol since Mac OS X 10.4, and a Windows driver, derived from Apple's implementation, is available for Windows XP and subsequent operating system versions.
Wireless MIDI
Systems for wireless MIDI transmission have been commercially available since the 1980s. Several contemporary transmitters facilitate the wireless conveyance of MIDI and OSC signals via Wi-Fi and Bluetooth technologies. iOS devices are capable of operating as MIDI control surfaces, leveraging Wi-Fi and OSC protocols. Furthermore, an XBee radio offers a viable option for constructing a DIY wireless MIDI transceiver. Similarly, Android devices can function as comprehensive MIDI control surfaces, employing various protocols over Wi-Fi and Bluetooth.
MIDI 2.0
ABC notation
- ABC notation
- Digital piano
- Electronic drum module
- Guitar synthesizer
- List of music software
- MIDI mockup
- MusicXML
- Music Macro Language
- SoundFont
- Synthetic music mobile application format
Notes
References
The MIDI Association, archived on February 19, 2018, at the Wayback Machine.
- The MIDI Association Archived 19 February 2018 at the Wayback Machine
- English-language MIDI specifications are available from the MIDI Manufacturers Association, archived on June 1, 2016, at the Wayback Machine.