A controller is a device used to send control information to other equipment without generating sound on its own. It allows parameters such as notes, effects, presets, or levels to be adjusted remotely, often using footswitches, knobs, sliders, or keys.

Controllers are widely used in modern music setups to manage pedals, processors, synthesizers, and software. They enable complex systems to be operated easily and consistently, especially in live performance and studio environments where hands-free or centralised control is needed.