A synthesizer (often abbreviated as synth, also spelled synthesiser) is an electronic musical instrument that generates electric signals that are converted to sound through instrument amplifiers and loudspeakers or headphones. Synthesizers may either imitate traditional musical instruments like piano, Hammond organ, flute, vocals; natural sounds like ocean waves, etc.; or generate novel electronic timbres. They are often played with a musical keyboard, but they can be controlled via a variety of other input devices, including music sequencers, instrument controllers, fingerboards, guitar synthesizers, wind controllers, and electronic drums. Synthesizers without built-in controllers are often called sound modules, and are controlled via USB, MIDI or CV/gate using a controller device, often a MIDI keyboard or other controller.

A ribbon controller or other violin-like user interface may be used to control synthesizer parameters. The idea dates to Leon Theremin's 1922 first concept and his 1932 Fingerboard Theremin and Keyboard Theremin,  Maurice Martenot's 1928 Ondes Martenot (sliding a metal ring),  Friedrich Trautwein's 1929 Trautonium (finger pressure), and was also later utilized by Robert Moog. The ribbon controller has no moving parts. Instead, a finger pressed down and moved along it creates an electrical contact at some point along a pair of thin, flexible longitudinal strips whose electric potential varies from one end to the other. Older fingerboards used a long wire pressed to a resistive plate. A ribbon controller is similar to a touchpad, but a ribbon controller only registers linear motion. Although it may be used to operate any parameter that is affected by control voltages, a ribbon controller is most commonly associated with pitch bending.  Fingerboard-controlled instruments include the Trautonium (1929), Hellertion (1929) and Heliophon (1936), Electro-Theremin (Tannerin, late 1950s), Persephone (2004), and the Swarmatron (2004). A ribbon controller is used as an additional controller in the Yamaha CS-80 and CS-60, the Korg Prophecy and Korg Trinity series, the Kurzweil synthesizers, Moog synthesizers, and others.  Rock musician Keith Emerson used it with the Moog modular synthesizer from 1970 onward. In the late 1980s, keyboards in the synth lab at Berklee College of Music were equipped with membrane thin ribbon style controllers that output MIDI. They functioned as MIDI managers, with their programming language printed on their surface, and as expression/performance tools. Designed by Jeff Tripp of Perfect Fretworks Co., they were known as Tripp Strips. Such ribbon controllers can serve as a main MIDI controller instead of a keyboard, as with the Continuum instrument.

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