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MIDI which means Musical Instrument Digital Interface is a connectivity standard for transmitting digital instrument data. It is mainly utilized by computers, electronic keyboards and synthesizers. It is also supported by other instruments like beatboxes, electronic drums and digital stringed instruments like guitars and violins.
MIDI is a protocol designed for recording and playing back music on digital synthesizers, supported by many types of personal computer sound cards. It’s originally designed to control one keyboard from another. It was quickly adopted for the personal computer. It sends data about how music is created. The command set contains note-ons, note-offs, key velocity, pitch bend and other methods of controlling a synthesizer. The sound waves created are those already saved in a wavetable in the receiving instrument or sound card.
With a program that offers this interface, you can produce music using a standard keyboard or other input devices. You can play your MIDI-conforming creation with the same or another program and a sound card as a music synthesizer. The MIDI program may have a graphical user interface that looks like a sound studio control room. Many sound cards come as a package with MIDI software.
MIDI data contains different kinds of information. When a single key on a synthesizer is pressed, it sends the note played, the velocity or how firm the note is pressed and how long the note is held. If several notes are played at once, the MIDI data is sent to all the notes simultaneously. Other information that may be transmitted over a MIDI connection includes the instrument ID, sustain pedal timings and controller data like pitch bend and vibrato.
When a synthesizer is connected to a computer through a MIDI connection, the notes played can be recorded by Digital Audio Workstation (DAW) software in MIDI format. The MIDI information can be played back by transmitting the recorded MIDI notes to the keyboard, which outputs them as audio samples like piano or strings. Most DAW software supports MIDI editing, allowing you to adjust the timing and velocity of individual notes, change their pitch, add or delete notes. MIDI information is often displayed in a digital format, with lines representing each note played. Many programs can translate MIDI information to a musical score.
A MIDI recording has instrument data and the notes played. The actual sound is played back using samples from real instruments. For example, a MIDI track recorded as a song for piano can be played back with a guitar sound by changing the output instrument.
Before, MIDI connections utilized MIDI cables connected to a 5-pin MIDI port on each device. Now, most of the MIDI devices have standard computer interfaces like USB or Thunderbolt ports. These modern interfaces offer more bandwidth than traditional MIDI ports, allowing more tracks with more data to be sent at once.
The MIDI protocol utilizes eight-bit serial transmission with one start bit and one stop bit. It has a 31.25 Kbs data rate and is asynchronous. Connection is made through a five-pin DIN plug, where three pins are used.
The MIDI standard outlines 128 General MIDI (GM) instruments, which are existing on most computers as software instruments. The sound of each GM instruments may vary between different computers and keyboards because the samples used for the instruments may be different, but the GM instrument ID is standard across devices. For example, GM instrument #1 is assigned to an acoustic piano, #20 is assigned to a church organ and #61 is assigned to a French horn. Modern synthesizers include hundreds or even thousands of other instruments that can be chosen, most of which offer more genuine sound than the GM options.