MIDI (Musical Instrument Digital Interface) is a communication protocol by which computers and musical instruments can communicate. With MIDI computers, music instruments, sound cards etc. can send and receive instructions from and to each other.
History
MIDI was born in the early 1980's when electronic instrument makers, primarily in the US and Japan, recognized that their instruments must be able to talk to one another. After the details were worked out, manufacturers soon began to include electronic circuitry in their equipment that allowed them to understand the instructions MIDI used.
Before long, nearly every instrument maker in the world had adopted the standard, and though there have been refinements and modifications to MIDI along the way, even the earliest MIDI instruments are still capable enough to be used today. Since its adoption, MIDI has dramatically changed the way music is created, performed and recorded.
What is MIDI
MIDI is a universally accepted standard for communicating information about a musical performance by digital means. It has both a hardware and software component, and though it could be used for sending information about many other things, such as the control of lighting in a theatre, it was originally developed to transmit instructions about music.
Like a music score MIDI transmits instructions that must be acted on by some device that can make sound. While a piano or guitar player will interpret the music score and produce the sound required, in MIDI it is most likely a synthesizer or drum machine that will react to the information.
MIDI is used both for realtime control of devices; and as files, where all the instructions are saved to a computer file. MIDI does not actually transmit sound electronically. Instead, its information is used in the sound-producing devices (synthesizers, drum machines, sound card etc.), that will create the sound you hear.
A MIDI transmission consists of a series of signals, called bits, that pass through a MIDI cable. These signals are electrical impulses that represent the 1's and 0's that make up the language of computers. When the impulses reach their destination (a device) the device interprets them as a series of instructions that usually result in the production of a sound.
The bits in the MIDI transmission move at 31,250 per second, and are transmitted in a serial manner, meaning one after another. Every bit does not represent a different note or event, however. Bits are grouped into strings of 10 to create MIDI messages.
MIDI messages are actually eight bits (= one byte). When messages are being transmitted, two extra bits, called the stop and start bits, are added to the beginning and end of the byte, hence the 10 bit length of most events.
MIDI messages detail specific aspects of a musical performance:
• what notes should be heard
• how loud they should be
• what type of sound (trumpet, drum, flute) should play the notes, etc.
while others are more general in nature.
Together, MIDI messages represent an entire language of musical actions, and can be used to control all details of a complete symphony or a simple hymn.