IMPORTANT: Some of the information in this section diverges from the official MMA/AMEI MIDI specifications in terminology and in technical detail. Developers interested in maximizing interoperability are encouraged to work directly from the official MMA/AMEI specifications.

There are two sides to MIDI 1.0: the hardware transport specification describing the electrical and mechanical connection, and the message format specification.

Hardware Transport (Electrical and Mechanical Connections)

MIDI ports and cable.

The MIDI standard consists of a communications messaging protocol designed for use with musical instruments, as well as a physical interface standard. It consists physically of a one-way (simplex) digital current loop serial communications electrical connection signaling at 31,250 bits per second. One start bit (must be 0), eight data bits, no parity bit and one stop bit (must be 1) is used. MIDI ports and cable. ... MIDI ports and cable. ... Look up Communication in Wiktionary, the free dictionary. ... Message in its most general meaning is an object of communication. ... For other senses of this word, see protocol. ... An electrical connector is a device for joining electrical circuits together. ... A simplex communication system is one where all signals flow in one direction. ... A digital system is one that uses discrete values (often electrical voltages), especially those representable as binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (ie, as in an analog system). ... A current loop describes two different electrical signalling schemes. ... In telecommunications and computer science, serial communications is the process of sending data one bit at one time, sequentially, over a communications channel or computer bus. ... In telecommunication, signaling has the following meanings: The use of signals for controlling communications. ... In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ...

Only one end of the loop is referenced to ground, with the other end "floating", to prevent ground loops which may otherwise cause interference and hum in analog audio signals. The current loop on the transmitter side drives the LED of an opto-coupler on the receiver side. This means the devices are, in fact, optically isolated. The opto-coupler must be a high-speed type. As most opto-couplers have asymmetrical positive-going and negative-going slew rates, they slightly alter the signal's duty cycle. If several MIDI devices are connected in series by daisy-chaining the MIDI THRU to the next device's MIDI-IN, the signal gets more and more distorted, until receive errors occur due to pulse narrowing. An opto-isolator is a device that uses optical techniques to electrically isolate two related circuits, typically a transmitter and a receiver. ... An opto-isolator integrated circuit Schematic diagram In electronics, an opto-isolator (or optical isolator, optocoupler) is a device that uses a short optical transmission path to transfer a signal between elements of a circuit, typically a transmitter and a receiver, while keeping them electrically isolated — since the signal goes... Symmetry is a characteristic of geometrical shapes, equations and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. ... In electronics, the slew rate is a nonlinear effect in amplifiers. ... In telecommunication and electronics, the term duty cycle has the following meanings: The duty cycle D is defined as the ratio between the pulse duration () and the period (T) of a rectangular waveform In a periodic phenomenon, the ratio of the duration of the phenomenon in a given period to... Daisy chain Daisy chain A daisy chain, in the most elementary sense, is a garland created from the daisy flower, generally as a childrens game. ... A MIDI-THRU (output) is an auxiliary output for MIDI signals, mostly found on musical instruments such as synthesizers. ... A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. ...

MIDI connectors are standard 5-pin 180° DIN connectors which at one time were a de facto European standard for audio interconnection. Over time the simpler American RCA phono jack has left MIDI as the only place where DIN is commonly encountered in modern equipment. Standard size DIN connectors were also used for computer keyboard connections from the early 80s through the late 90s and have generally been replaced by mini-DIN connectors, and more recently by USB connectors. 5 pin 180° DIN connector 4 pin Mini-DIN S-Video connector Speaker DIN line socket (left) and plug DIN connectors are multi-pin electrical connectors based on a DIN standard. ... De facto is a Latin expression that means in fact or in practice. It is commonly used as opposed to de jure (meaning by law) when referring to matters of law or governance or technique (such as standards), that are found in the common experience as created or developed without... This article does not cite its references or sources. ... Note: USB may also mean upper sideband in radio. ...

Some computers or their sound cards have 15-pin D-subminiature connectors, called game ports, that can be used for MIDI IN/MIDI OUT. The connector supports both MIDI and analog joystick functions. Access to the MIDI signals is provided by a short adapter cable that converts the D-subminiature pinout into DIN connectors. The recommended method of connecting two 5-pin DIN cables to a 15-pin D-subminiature computer port can be found at the MIDI.org web site. The MIDI specification very conservatively states that the maximum distance MIDI can be transmitted is 15 meters (50 feet), but it can normally go much further. It has been suggested that DE-9 be merged into this article or section. ... A PCI based soundcard with a DA-15 connector The game port is the traditional connection for video game input devices on an x86-based PCs. ... Joystick elements: 1. ...

There is a USB connection standard and a standard for MIDI over Ethernet and Internet called RTP MIDI being developed by the IETF. See external links below for further information. Note: USB may also mean upper sideband in radio. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operates at many speeds for local area networks (LANs). ... The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ...

Most MIDI capable instruments feature a MIDI IN, MIDI OUT, and occasionally a MIDI THRU connection in the form of five-pin DIN connectors. In order to build a two-way physical connection between two devices, a pair of cables must be used. The MIDI THRU jack simply echoes the signal entering the device at MIDI-IN. This makes it possible to control several devices from a single source.

The 1985 Atari ST was the first home computer to sport the original five-pin DIN format, making it a very popular platform for running MIDI sequencer software. Most PC soundcards from the late 1990s had the ability to terminate a MIDI connection, usually through a MIDI IN/MIDI OUT converter on the game port. The game port has been supplanted in the modern PC by USB devices, and so typically a PC owner will need to purchase a MIDI interface that attaches to the USB or FireWire port of their machine to use MIDI. The Atari 520ST Atari 1040STF with SC1224 color monitor The Atari ST is a home/personal computer that was commercially popular from 1985 to the early 1990s. ... Children playing on a Amstrad CPC 464 in the 1980s. ... In the field of electronic music, a sequencer was originally any device that recorded and played back a sequence of control information for an electronic musical instrument. ... A sound card is a computer expansion card that can input and output sound under program control. ... The 6-pin and 4-pin FireWire Connectors FireWire is Apple Inc. ...

Message Format

Every MIDI connection is a one-way connection from the MIDI Out connector of the sending device to the MIDI In connector of the receiving device. Each such connection can carry a stream of MIDI messages, with most messages representing a common musical performance event or gesture such as note-on, note-off, controller value change (including volume, pedal, modulation signals, etc.), pitch bend, program change, aftertouch, channel pressure. All of those messages include channel number. There are 16 possible channels in the protocol. The channels are used to separate "voices" or "instruments", somewhat like tracks in a multi-track mixer. The horizontal axis shows frequency in Hz Loudness is the quality of a sound that is the primary psychological correlate of physical intensity. ... A short grand piano, with the top up. ... Portamento is a musical term currently used to mean pitch bending or sliding, and in 16th century polyphonic writing refers to a type of musical ornamentation. ... Keyboard expression often shortened to expression is the ability of the keyboard of a keyboard instrument to respond to the dynamics of the music. ...

The ability to multiplex 16 "channels" onto a single wire makes it possible to control several instruments at once using a single MIDI connection. When a MIDI instrument is capable of producing several independent sounds simultaneously (a multitimbral instrument), MIDI channels are used to address these sections independently. (This should not be confused with "polyphonic"; the ability to play several notes simultaneously in the same "voice".) Often used in the realm of digital keyboard synthesisers, an instrument that is multitimbral is one which allows you to combine several voices or timbres at the same time. ... In music, the word texture is often used in a rather vague way in reference to the overall sound of a piece of music. ...

In more detail, MIDI 1.0 defines several basic message types of channel messages:

• Note messages can represent any note from '''C (i.e. five octaves below middle C or 8.176 Hz in common Western musical tuning; designated as MIDI note 0) to g'''''' (i.e. five octaves above the G above middle C or 12,544 Hz; designated as MIDI note 127) with precision down to the semitone. A note on message starts a note, and separate note off message is needed to end it.

• Pitch-bend messages range in ±2 semitones (sometimes adjustable with Registered Parameter Numbers), with precision of 1/8192 semitone (The human ear cannot hear the difference between adjacent pure tones that differ by less than 1/20 semitone). Most synthesizers allow you to adjust the pitch bend range over several octaves.

• "Control Change" messages (frequently wrongly called Continuous Controller) are quite versatile; they are usually generated by a musician using knobs, sliders, footswitches, or pressure on a physical MIDI controller (or MIDI-equipped instrument). While the response to these messages is generally totally up to the receiving device, they are typically used to change the tone, timbre, or volume of an instrument's sound. In non-musical applications of MIDI, Control Change messages can be used to move motorized faders, to dim lights, or even to move a motorized joint in an animatronic figure.

• Program change messages are sent to an instrument on a particular channel to instruct it to recall another patch, or program. The MIDI protocol uses 7 bits for this message, supporting only 128 program changes. Many devices which are more modern than the MIDI specification store far more than 128 programs. To overcome the limitation, a bank-switching method has been added to the spec (Each bank of 127 programs can be selected using a controller message, enabling access to 127² = 16129 programs).

• Aftertouch messages (also known as Poly Pressure messages) are sent in some instruments to indicate pressure changes on the note while it is being played. Similarly, channel pressure changes the pressure for the entire instrument, not just one note. The channel pressure messages are more commonly implemented in most synthesizers, while the individual pressure sensors that aftertouch messages require are reserved mainly for expensive, high-end synthesizers.

In addition to the channel-based messages, there are system-related messages not addressed to any particular channel. These include: In music, an octave (sometimes abbreviated 8ve or 8va) is the interval between one musical note and another with half or double the frequency. ... The hertz (symbol: Hz) is the SI unit of frequency. ... In music, there are two common meanings for tuning: Tuning practice The act of tuning an instrument or voice. ... A semitone (also known in the USA as a half step) is a musical interval. ... Hearing, or audition, is one of the traditional five senses, and refers to the ability to detect sound. ... In music, timbre, also timber (from Fr. ...

• Manufacturer's System Exclusive messages (also known as Manufacturer SysEx, Manuf Sysx, etc.) are defined by the manufacturer of the sequencer/synthesizer and can be any length. These messages are commonly used to send non-MIDI data over a MIDI connection, such as a synthesizer instrument sample or settings and a sequencer's memory dump. Because they are defined by the device's manufacturer, they are mainly used for backup purposes and rarely (if ever) useful in another MIDI device.

• Real Time System Exclusive messages include the significant MIDI Show Control extension which enables all types of entertainment equipment to easily communicate with each other through the process of show control.

• System messages contain meta-data about other MIDI messages. A sequencer, for example, often sends MIDI clock messages during playback that correspond to the MIDI timecode, so the device receiving the messages (usually a synthesizer) will be able to keep time. Also, some devices will send Active Sense messages, used only to keep the connection between the sender and the receiver alive after all MIDI communication has ceased.

MIDI can be used to provide facilities for playing in musical tunings different from the 12 tone per octave, equal-tempered tuning used in most western musical traditions. However, apart from using pitch-bend to control each note, these features have not been implemented by all instrument manufacturers. MIDI Show Control, or MSC, is a significant Real Time System Exclusive extension of the international Musical Instrument Digital Interface (MIDI) standard. ... Show control is the use of technology to link together and operate multiple entertainment control systems in a coordinated manner. ... In music, there are two common meanings for tuning: Tuning practice The act of tuning an instrument or voice. ...

Low bandwidth

MIDI messages are extremely compact, due to the low bandwidth of the connection, and the need for real-time accuracy. Most messages consist of a status byte (channel number in the low 4 bits, and an opcode in the high 4 bits), followed by one or two data bytes. However, the serial nature of MIDI messages means that long strings of MIDI messages take an appreciable time to send, at times even causing audible delays, especially when dealing with dense musical information or when many channels are particularly active. Wikipedia does not have an article with this exact name. ... In computer science a byte is a unit of measurement of information storage, now usually considered to contain eight bits. ... Microprocessors perform operations using binary bits (on/off/1or0). ... It has been suggested that this article be split into multiple articles accessible from a disambiguation page. ...

To further optimize the data stream, "Running status", a convention that allows the status byte to be omitted if it would be the same as that of the previous message, helps to mitigate bandwidth issues somewhat.