When you strike a key on the keyboard, the keyboard transmits a note-on message. This message has three main parts: a channel number (1 through 16), a note number, and a velocity value. The note number tells which key you played. Middle C, for instance, is note 60, and most five-octave keyboards go from note 36 at the low end to note 96 at the high end. The velocity is a number between 1 and 127. When you strike the key, most keyboards sense how rapidly the key moves toward the bottom of its travel: This measurement determines the MIDI velocity. When you lift your finger from the key, the keyboard sends a note-off message. Again, this has a channel and a note number. Note-off messages can also have velocity values; some keyboards can sense how rapidly you lift your finger. But note-off velocity is not very important musically: Most instruments just ignore it.