A MIDI message that tells an instrument to play a note. It consists of three bytes: a status byte that identifies itself as a “note on” message and includes the MIDI channel affected; a data byte that identifies the MIDI note number to be played; and a second data byte that dictates the velocity with which the note is to be struck.
In binary data, the status byte for a Note On message transmitted on MIDI channel 1 would be 1001 0000. The data byte identifying Middle C would read 0011 1100. And the velocity data byte representing a velocity of 127 (the highest possible velocity represented in MIDI) would appear as 0111 1111.
Many early MIDI devices used a Note On message with a velocity of “0” to represent the end of a note. This avoided the expense of installing keyboard sensors that could recognize the release (or Note Off) of each note.
Some large sample libraries, such as the Miroslav Vitous or Gary Garritan Orchestral Strings, employ Note On messages that are out of the pitch range of a particular instrument to execute program changes or different articulations. For example, some violin instruments can be switched from marcato, pizzicato, and long looped samples simply by pressing notes that are a couple of octaves below the violin’s lowest pitch.