Note On & Note Off Messages
In MIDI systems, the activation of a particular note and the release of the same
note are considered as two separate events. When a key is pressed on a MIDI
keyboard instrument or MIDI keyboard controller, the keyboard sends a Note On
message on the MIDI OUT port. The keyboard may be set to transmit on any one of
the sixteen logical MIDI channels, and the status byte for the Note On message
will indicate the selected channel number. The Note On status byte is followed
by two data bytes, which specify key number (indicating which key was pressed)
and velocity (how hard the key was pressed). The key number is used in the
receiving synthesizer to select which note should be played, and the velocity is
normally used to control the amplitude of the note.
When the key is released,
the keyboard instrument or controller will send a Note Off message. The Note Off
message also includes data bytes for the key number and for the velocity with
which the key was released.
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