What is MIDI? (Musical Instrument Digital Interface)

Midi Cable

What’s a MIDI?

The acronym MIDI stands for Musical Instrument Digital Interface. It is a communications protocol developed in 1983 for electronic instruments to communicate with one another, allowing a single musician to sound as if they are playing multiple instruments at the same time. This revolutionary technology drastically changed the music industry, both from a recording viewpoint and for live performances.

MIDI requires a controller, which is the instrument that provides the information for the rest of the devices to decode into music. As originally created, this controller was most often an electronic keyboard. However, many other MIDI control devices have since been created, including woodwind, guitar, drum machines and even an electronic tablet. 

The controller doesn’t actually send music to the devices which are connected to it. Instead, it sends a series of instructions, which tell the device how to play the music. These instructions will include note, pitch, velocity, volume, vibrato, audio panning, cues and clock singles. From this information, the MIDI device plays sound files, called samples, which are stored in its library, producing the desired music.

While the system is not perfect, it produces very credible sounds. A major factor in the quality of the sound produced is the quality of the samples which are recorded. These samples are actual recordings of instruments, some of which have been altered electronically, that are stored in the MIDI device’s memory. Early MIDI devices used the Yamaha standard, which did not provide enough memory for high quality samples. Newer equipment has abandoned this standard, improving the sample quality to the point that a trained musician may have trouble determining whether the sound produced is from the instrument or a MIDI device.

Elements of a MIDI System

A MIDI system consists of several electronic devices connected together. A single device, such as a keyboard, cannot utilize MIDI, even though it is MIDI compatible. It is the communication of that keyboard with other devices that makes MIDI work.

Controller – A MIDI controller is the device that the musician plays. It turns the notes played by the musician, including all the data which pertains to those notes, and converts it into the MIDI message for transmission to other devices. One MIDI controller can provide up to 16 separate channels of information, each of which is can be routed to a separate device.

Sequencer – A MIDI sequencer is a device that can record, edit and play back music, based upon the MIDI messages. This requires much less memory than recording the music itself, as the only thing which is recorded is the data. When played, the data is used to allow the sequencer to create the music, adding waveforms from the samples it has in memory.

This provides the capability of doing a number of things to the recorded music, including changing the tempo, without affecting the pitch, changing the pitch without changing the tempo, and correcting errors. However, the biggest use of sequencers is to record background music for a musician to use when playing solo. This saves the musician the cost of paying for backup musicians.

MIDI Effect Unit or Sound Module – A MIDI effect unit takes the MIDI message and converts it to an electronic sound wave. All of the information is provided by the controller or sequencer, with the exception of the sample waveforms. Due to differences in effect units, the same MIDI message can produce different sounds, even sounding like different instruments, when connected to different MIDI effect units.

midi drum maching connections

Drum Machine – A drum machine is a special type of MIDI “instrument” which is designed to simulate a musician playing a drum kit. It has a number of pre-recorded MIDI sequences in its memory, which can be altered by tempo. Additionally, the musician has the option of adding fill notes, intro sequences, closing sequence, and bridges.

Connecting MIDI Equipment

MIDI devices have interface connectors, allowing them to be connected together. This connection is typically a “daisy chain” allowing the signal from one MIDI controller to reach a number of MIDI devices. There are three types of MIDI connections on controllers and devices, MIDI Out, MIDI In and MIDI Through. Information only passes in one direction, from the MIDI controller to the other devices. 

The MIDI Out connection is used to provide MIDI messages from the controller to the various devices in the setup. This is connected to the MIDI In connection on the next device in the series. To connect additional devices, the MIDI Through connector from the second device is connected to the MIDI In on the third device.

The MIDI connector itself is a 180 degree 5 pin DIN connector. For most applications, only three of the pins are used, one for a ground and the other two, a twisted pair, for data. There is no error detection built into MIDI protocols, so the maximum range for a MIDI cable is 15 meters (50 feet).

MIDI Management Devices

One of the problems with MIDI is caused by the daisy-chain connection. Each device delays the signal slightly as it is passed down the chain. This can cause timing problems, as the later devices in the chain will be playing the note slightly later than the earlier ones.

This problem can be solved by the use of a MIDI Management Device. This device acts as a hub for MIDI messages, receiving them from the controller, and sending them out to all devices at the same time.

MIDI switchers allow the connection of multiple MIDI management devices to one MIDI controller, allowing multiple setups, without rewiring.

MIDI With Computers

Perhaps the most exciting advances that MIDI has provided to the music industry have been in providing an interface between electronic instruments and computers. This allows the computer with the right software installed to act as a MIDI sequencer, recording, editing and playing music. Even more importantly, the computer can be used for composing music, allowing even those with limited musical talent and ability to produce music to be played through other MIDI devices.

MIDI files, created on a computer, can be uploaded to MIDI controllers. This allows the musician to create his background music in the home studio, then take his MIDI setup to a performance or recording studio for use.


There is no saying where MIDI will lead in the future. Although efforts are underway to create a new protocol to replace or upgrade MIDI, there is so much equipment currently available that uses the existing MIDI protocol that replacing it would be difficult. Perhaps two systems will exist in parallel for some years, but unless the new protocol provides considerably capability not currently available, it is unlikely that MIDI will be fully abandoned.


Rich Murphy