What is MIDI? - Controller, Interface & Songs

Instructor: Greg Simon

Greg is a composer and jazz trumpeter. He has a doctorate from the University of Michigan and has taught college and high school music.

This lesson will teach you about MIDI, the musical computer language that's defined electronic music since the 1970s. You'll learn important terminology and concepts, see how the MIDI system works and get your groove on with a few MIDI-using tunes.

Meaning and Power of MIDI

What if your piano wasn't just a piano? What if it could be a whole orchestra? Although it contains less than 100 black and white keys, what if you could use your piano to create screaming trumpets, warm and woody cellos, bird-calling flutes and piccolos? That's the power of MIDI (pronounced middy), an acronym for musical instrument digital interface.

MIDI turns a musical action, like pressing a piano key, into computer code that can be read by other systems; it can connect your keyboard to a library of millions of different sounds, putting an entire orchestra at your fingertips. This lesson will look under the hood at what makes MIDI work, its history and some starting points for MIDI-based listening.

How MIDI Works

MIDI refers to a digital language shared by computers and some electronic instruments. Computers play back MIDI data using software or devices, called sequencers, which are designed to read MIDI information. The data can be composed on the computer itself or performed on a MIDI musical instrument, called a controller, and then sent to the sequencer.

A MIDI Performance Setup
An electronic MIDI setup. Photo by Chris Carter.

Although electronic music and instruments were already quite popular by the 1970s, each manufacturer used their own programming language, which made it nearly impossible to use instruments or systems by multiple makers. MIDI was the answer: a shared language which all electronic music manufacturers could use to program their instruments and computers. This made it possible for musicians to string together devices from different makers in a single setup. A team of designers from several major music companies worked together to craft the basic language in the early 1980s, and the rest is history.

MIDI Signals

A MIDI signal contains a ton of information about its sounds, but the most important parameters it defines are:

  • The pitch of each sound, or how high or low we perceive it
  • The duration of each note, or how long it lasts before the note is released
  • The velocity, or the volume of each sound

The higher the velocity of a sound, the louder it seems. If you have access to a piano keyboard, strike one of the keys slowly, then strike the same key fast. What happens?

A MIDI signal can provide information about multiple 'instruments', each with their own pitch, rhythm and velocity; these instruments are referred to as channels. Generally one MIDI connection has capacity for up to 16 individual channels.

Sequencers play back MIDI data using sound banks, which are libraries of synthetic sounds. Some of these sounds are designed to mimic instruments of the orchestra, while others are modeled after electronic instruments. Some sound banks even feature sound effects like cats meowing, dogs barking and natural sounds like thunderclaps. Devices called samplers can record sounds, then map them to a MIDI instrument; those sounds can then be played back on a sequencer.

Flow of a MIDI Signal
A MIDI signal flowchart, from controller to sequencer with sound bank. Image by Greg Simon.

The Musical Instruments

A MIDI controller often looks like an acoustic musical instrument, such as a piano or a drum set; however, it doesn't have the capability to make sound by itself. Instead, a MIDI controller translates the music played upon it into MIDI information, which is then fed into a sequencer to produce sound. The sequencer is either onboard, which means it's part of the controller's system itself, or outboard, which means it's found on another computer connected to the controller by a cable. Controllers which produce sound using their own onboard sequencers are sometimes called MIDI synthesizers.

A Small MIDI Controller
A MIDI controller. Photo by allangothic on Wikimedia Commons.

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