A MIDI message that tells the receiver to begin sounding a note. The message contains the note number of the note, and a velocity value that encodes how rapidly or with how much force the key was pressed. The receiver is supposed to use the velocity value to scale the amplitude and/or attack time of the note sounded; it may also use the value to perform other functions, such velocity switching on a sampler. The note on message does not specify a duration for how long the note is to be held; it is indefinite until a corresponding note off message containing the same note number (or an all notes off) is received.