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A sound module is an electronic musical instrument without a human-playable interface such as a piano-style musical 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, guitar controllers and electronic drum pads are also used). Controllers are devices that provide the human-playable interface and which may or may not produce sounds of their own. Another common way of controlling a sound module is through a sequencer, which is computer hardware or software designed to record and playback control information for sound-generating hardware (e.g., a DJ may program a bassline and use the sound module to produce the sound). 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, which includes special ports (jacks) and cables.
Sound modules are often rack-mountable, but might also have a table-top form factor, particularly when the intended user is a DJ or record producer. The height of a sound module is often described in rack units ("U") or unit. Small sound modules are mostly 1U in height, the larger models a multiplication e.g. 2U or 3U. Despite their name, most sound modules do not produce any audible sound until their output is plugged into a keyboard amplifier or a PA system.
There are a wide variety of sound modules, ranging from more generalist modules that can be used for a number of controllers or instruments (e.g., a rack mount synthesizer with hundreds of commonly used presets of instrument sounds, from piano and organ to synth brass and string pads) to specialized modules designed for use with wind controllers, electronic drum pads, digital accordions, or to produce clonewheel organ sounds.
Hardware sound modules have largely been replaced by software synthesizers, due to the increased speed and processing power of computers and their decrease in price. Nevertheless, some DJs, EDM musicians and record producers continue to use vintage 1980s sound modules like the Yamaha TX16W (1988) for their unique, retro sound.
A sound module may also be referred to as "tone generator", "synth module", "MIDI sound generator", "MIDI module", "expander", or "rack-mount synthesizer". With electronic drums, the sound module is sometimes colloquially called the "brain".
Technologies and types
Electronic drum modules are sound modules which specialize in drumkit and percussion sounds. Drum modules may be triggered by external trigger pads or pickups attached to an acoustic drum as well as through MIDI controller pads. Drum modules are distinguished from drum machines through their lack of dedicated onboard triggers and lack of an integrated sequencer.
Clonewheel organ modules are usually tabletop-style devices that enable keyboardists to recreate the sound of a tonewheel-based Hammond organ using any MIDI keyboard or MIDI-equipped stage piano. Organ modules may have drawbars and controls for a simulated Leslie speaker (a rotating horn and low-end baffle) effect.
Wind controller modules are specialized synth modules that are designed to work with wind controllers. They typically support legato wind-style playing and can respond to the unique controller inputs, which sense breath, biting on the mouthpiece, and pressing keys. Wind controller players may use a specialized wind controller module such as the Yamaha VL70-m module or its predecessors, the VL-1 or VL-7. As well, wind controller players may use general purpose rack synths such as the Yamaha Motif XS Rack, Roland Fantom X, or the Roland Integra-7 rackmount MIDI sound module; however, these general use synths require extra wind sounds or "patches" to work well with wind controllers.
An accordion module, which is designed for use with a MIDI-equipped digital accordion, focuses on providing synthesized and/or sampled accordion sounds (and sounds for related bellows-pumped instruments, such as bandoneon and concertina). Like other specialized sound modules, accordion modules also have other sounds (piano, string orchestra, flute, etc). Moreso than for other sound modules, accordion modules are likely to also have music sequencer, drum machine, and backing track features, to enable a performer to do a one man band show. Accordion modules are manufactured by firms such as Ketron and Soltron.
Because most electronic instruments are designed in a modularized way, manufacturers often release a sound module version of their fully integrated instruments. For example, the 1980s-era DX-7 synthesizer/keyboard was also sold as a standalone "sound module", the TX-7. 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, instrument and other 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.
The front of a rackmount sound module, or the top for tabletop units, typically contains a small screen or panel to provide information to the user (e.g., an electric piano sound may be called EP 1). This may be an LCD panel (which may or may not be backlit) or an LED alphanumeric display. This may be supplemented with LED indicators to show the status of various features. In some models, LED indicators are embedded within a translucent button, so pressing the button shows its status on the button. There is usually a volume control, some types of buttons or knobs for selecting sounds and changing settings, and a power button. The smallest, simplest piano modules may have only a volume knob and a knob to scroll through several piano sounds. The most complex synth modules may have a large number of knobs, buttons, and faders to control oscillators, filters, and amplitude settings.
The rear panel usually contains 1/4 inch left and right audio outputs and one or more 5-pin MIDI inputs. Some units may have MIDI thru connections, which can be used to chain synth devices. In the 2010s and 2020s, some synth modules have one or two USB connections. Some synth modules may have left and right XLR outputs and one or more pedal inputs (for a sustain pedal and expression pedal). The front panel may also have a headphone jack, USB port, or another port for making connections. Some synth modules may have an XLR input for a vocal mic, for routing through a vocoder.
Some 2010s and 2020s-era synth modules can be connected to a computer (laptop, tablet, etc), to allow the user to use editing software to make advanced changes to settings or sounds. Many synth modules can have new sounds loaded. In 1980s-era modules, external tape players, cartridges, or floppy disks were used. In the 2000s (decade) and 2010s, USB connections were increasingly used to load new sounds. Some 2020s-era sound modules have a WiFi antenna connection to allow wireless loading of updates and new sounds.
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 and weight — a sound module takes up less room and weighs less than an instrument equipped with a controller, facilitating transportation and touring.
- Portability - a performer going on tour can bring only her/his sound modules, so long as a MIDI controller is provided as "backline" gear (e.g., a MIDI keyboard). Many professional studios have a MIDI stage piano on hand.
- Expandability — many sound modules can be expanded with sounds and memory.
- Troubleshooting – if a sound module in a rack case develops problems, just this one unit can be removed for repair or replacement, leaving the rest of a keyboard player's rig the same (e.g., other rack-mounted sound modules, power amps, etc.).
- Obsolescence cycles — when it becomes obsolete, a sound module can be replaced without changing a favorite controller, or vice versa.
- Roland MKS20: Piano sound module used by many bands in the 1980s to early 1990s. Based on the synth "engine" from RD1000 digital piano (the full version with a keyboard).
- Yamaha TX16W (1988): sound module with an ability to boot its operating system (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 the original OS.
- Roland Sound Canvas series (1991): first sound module to implement General MIDI standard with Roland GS extensions.
Difference from audio interfaces
Audio interfaces are often erroneously called sound modules. 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.