feedback

Influence of the outputs of a process on the inputs. It is the principle used in self-regulating control systems, from a simple thermostat and steam-engine governor to automatic computer-controlled machine tools. A fully computerized control system, in which there is no operator intervention, is called a closed-loop feedback system. A system that also responds to control signals from an operator is called an open-loop feedback system.

In self-regulating systems, information about what is happening in a system (such as level of temperature, engine speed, or size of workpiece) is fed back to a controlling device, which compares it with what should be happening. If the two are different, the device takes suitable action (such as switching on a heater, allowing more steam to the engine, or resetting the tools). The idea that the Earth is a self-regulating system, with feedback operating to keep nature in balance, is a central feature of the Gaia hypothesis.

feedback

In music, a continuous tone, usually a high-pitched squeal, caused by the overloading of circuits between electric guitar and amplifier as the sound of the speakers is fed back through the guitar pickup. Deliberate feedback is used in rock music.

The electric guitar innovator Les Paul used feedback in recording, as in ‘How High the Moon’ (1954), but it was generally regarded by producers as an unwanted noise until the Beatles introduced it on ‘I Feel Fine’ (1964). Both live and in recording, feedback was employed especially by the Who, Jimi Hendrix, and the Velvet Underground in the 1960s, and by noise and grunge bands in the 1980s and 1990s.

feedback

In communication, response from the person or group receiving information or a message. This may, for example, take the form of a critical response (negative feedback), or it may be an affirmative response (positive feedback).

feedback

In biology, another term for biofeedback: the influence of the outcome of one process upon the functioning of another process.