what is midi and how does it work?

Answer 1

Musical Instrument Digital Interface, or MIDI, is an industry-standard electronic communications protocol that defines each musical note or event in an electronic musical instrument or show device such as a synthesizer, precisely and concisely, allowing electronic musical instruments, computers and other show equipment to exchange data in real time. MIDI does not transmit audio—it simply transmits real time digital data providing information such as the type and intensity of the musical notes and technical cues played during a performance.

How MIDI works in a nutshell

- How MIDI channel messages work

When a note is played on a MIDI-aware instrument, it transmits MIDI channel messages. A typical MIDI channel message sequence corresponding to a key being struck and released on a keyboard is:

1. the user presses the middle C key with a specific velocity (which is usually translated into the volume of the note but can also be used by the synthesiser to set the timbre as well)
2. the user changes the pressure applied on the key while holding it down - a technique called aftertouch (can be repeated, optional)
3. the user stops playing the middle C note, again with the possibility of velocity of release controlling some parameters

Other performance parameters can be transmitted. For example, if the pitch wheel is turned, that information is transmitted using pitch bend MIDI channel messages. The musical instrument does this completely autonomously requiring only that the musician play a note (or do something else that generates MIDI messages).

All notes that a musical instrument is capable of playing are assigned specific MIDI channel messages according to what the note and octave are. For example, the Middle C note played on any MIDI compatible musical instrument will always transmit the same MIDI channel message from its 'MIDI Out' port. Which MIDI channel message and thus which binary digits will be transmitted upon playing of a certain note are defined in the MIDI specification and this comprises the core of the MIDI standard.

All MIDI compatible instruments follow the MIDI specification and thus transmit identical MIDI channel messages for identical MIDI events such as the playing of a certain note on the musical instrument. Since they follow a published standard, all MIDI instruments can communicate with and understand each other, as well as with MIDI-compatible software. The MIDI interface converts the current events transmitted by a MIDI musical instrument into binary numbers that the receiving musical instrument or computer can process. All MIDI compatible instruments have a built-in MIDI interface. Some computers' sound cards have a built-in MIDI Interface, others require external MIDI Interface usually connected to the computer via USB.

- How MIDI Show Control works

When any cue is called by a user (typically a Stage Manager) and/or preprogrammed timeline in a show control software application, the show controller transmits one or more Real Time System Exclusive messages from its 'MIDI Out' port. A typical MSC message sequence is:

1. the user just called a cue
2. the cue is for lighting device 3
3. the cue is number 45.8
4. the cue is in cue list 7

Answer 2

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