A
sound module is an
electronic musical instrument without a human-playable interface such as a
keyboard. Sound modules have to be operated using an externally connected device, which is often a
MIDI controller, of which the most common type is the musical keyboard (although
wind controllers and
guitar controllers are also used). Controllers are devices that provides the human-playable interface and may or may not produce sounds of its own, or a
sequencer, which is computer hardware or software designed to play electronic musical instruments. Connections between sound modules, controllers, and sequencers are generally made with
MIDI (Musical Instrument Digital Interface), which is a standardized protocol designed for this purpose.