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.

Sound modules may use any number of technologies to produce their sounds.A sound module may be a synthesizer, a sampler, or a rompler. Drum modules are sound modules which specialize in percussion sounds. Drum modules may be triggered by external trigger pads or pickups as well as through MIDI. Drum modules are distinguished from drum machines through their lack of dedicated on-board triggers and lack of an integrated sequencer. Sound modules are often rack-mountable, but might also have a table-top form factor. The height of a sound module is often described in U or unit. Small sound modules are mostly 1U in height, the larger models a multiplication e.g. 2U or 3U.