Introduction to Computer Music: Volume One

1. How does the MIDI system work? Page 3

MIDI Data Format

The majority of MIDI communication consists of multi-byte packets beginning with a status byte followed by one or two data bytes .Bytes are packets of 8 bits (0's or 1's). Status bytes begin with a '1' e.g. 1xxx xxxx--this is call 'set.' Data bytes begin with a '0' e.g. 0xxx xxxx--this is called 'reset.' Each byte is surrounded by a start bit and a stop bit, making each packet 10 bits long. Messages fall into the following five formats:

    • Channel Voice
      Control the instrument's 16 voices (timbres, patches), plays notes, sends controller data, etc.
    • Channel Mode
      Define instrument's response to Voice messages, sent over instrument's 'basic' channel
    • System Common
      Messages intended to all networked instruments and devices
    • System Real-Time
      Intended for all networked instruments and devices. Contain only status bytes and is used for syncronization of all devices. essentially a timing clock
    • System Exclusive
      Originally used for manufacturer-specific codes, such as editor/librarians, has been expanded to include MIDI Time Code, MIDI Sample Dump Standard and MIDI Machine Control

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