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README.md
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README.md

What's MIDI?

  • MIDI - Musical Instrument Digital Interface
  • A standard protocol for communication between computers and musical instruments.
  • Sends series of messages which are intepretted by a MIDI instrument.

MIDI messages

  • Made up of an 8-bit status byte (or command byte) which is generally followed by 1 or 2 data bytes.
  • Command byte: tells what type of message is being sent.
  • Data bytes: actual data that is sent with the command byte.
  • Two types of MIDI messages: System messages, Channel messages.
  • Channel -> an independent path over which messages travel to their destination.
  • A MIDI device has 16 channels.
  • Channel messages -> apply to a specific channel, channel number is included in the status byte.
  • Channel Messages may be further classified as being either Channel Voice Messages, or Mode Messages.
  • Channel Voice Messages: carries musical performance data.

Channel Voice Messages

Categories: Note On, Note Off, Polyphonic Key Pressure, Channel Pressure, Pitch Bend Change, Program Change, and the Control Change messages.

  • MIDI data bytes range from 0 to 127 (MSB is always 0).
  • MIDI command byte ranges from 128 to 255 (MSB is always 1).
  • Two types of bytes are differentiated by the MSB.
  • First half of the command byte (three bits after MSB) -> sets the type of command.
  • Last half of the command byte -> sets the channel number.

MIDI Commands

10000000 (128) = note off
10010000 (144) = note on
10100000 (160) = aftertouch
10110000 (176) = continuous controller
11000000 (192) = patch change
11010000 (208) = channel pressure
11100000 (224) = pitch bend

Note On

  • Sent when a key is pressed.
  • Consists of two pieces of info: which key was pressed (note) and how fast it was pressed (velocity).
  • Note is a number from 0 to 127. Middle C (C4) is 60.
  • Velocity is a number from 0 to 127. Describes volume of the note. (For some voices, different velocities create different timbres.)

Note Off

  • Sent when a key is released.
  • Also contain note information to ensure that it is signalling the end of the right note.
  • Sometimes a note off may contain velocity information too.

Aftertouch

  • The amount of pressure applied to a note.
  • Sent when a key is pressed.
  • Ranges from 0 to 127.