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A sound module (sometimes referred to as tone generator, synth module, MIDI sound generator, or rack-mount synthesizer) 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. The external device may be a controller, which is a device 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.
Compare with audio interface that is often erroneously called a sound module. The audio interface connects a computer to other devices; and software in the computer actually generates sound using samples or synthesis. The functionality of the computer and I/O device plus the software is a superset of a traditional sound module.
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.
A sound module has the same advantages over a fully integrated instrument as does any system with a modularized design:
- Cost — a sound module is cheaper than a comparable instrument equipped with a controller
- Space — a sound module takes up less room than an instrument equipped with a controller
- Expandability — many sound modules can be expanded with sounds and memory
- Obsolescence cycles — when it becomes obsolete, a sound module can be replaced without changing a favorite controller, or vice versa.
Because most electronic instruments are designed in a modularized way, manufacturers often release a sound module version of their fully integrated instruments. A sound module may have all the other features of the controller-equipped version, but it often has a smaller display or limited programming controls. In this case, sounds can be loaded through MIDI or external media. In some cases, sound modules have expanded capacity for sounds in comparison to the controller-equipped version.
Hardware sound modules have in recent years been replaced to a large extent with software equivalents, mainly due to the increased processing power of computers.
Notable sound modules
- Roland MKS20, Piano sound module used by many acts in the 80s to early 90s. Based on engine from RD1000.
- Yamaha TX16W (1988), sound module with an ability to boot OS from diskette; known particularly well for having a third-party OS codenamed Typhoon 2000 by NuEdge Development, a group of hackers who were dissatisfied with original OS.
- Roland Sound Canvas series (1991), first sound module to implement General MIDI standard with GS extensions.