Communications / Electroacoustics
Any process in which the output depends functionally on itself (i.e. on the input). Feedback may be positive or negative; positive when the SIGNAL feedback is in PHASE with the input signal, and negative when it is in phase opposition (i.e. out of phase) with the input. Positive feedback is normally undesirable for AMPLIFIERs, for while the GAIN is increased, it is usually at the expense of stability and FIDELITY. Negative feedback, while cancelling part of the input, improves FREQUENCY RESPONSE, lowers DISTORTION and NOISE.
Compare: ECHO, PHASING.
Feedback also refers to a process of behaviour modification in which information received about the behaviour and its effect influences future behaviour. This concept plays an important role in the field of cybernetics, and has influenced the design of servomechanisms, theories of learning, and work in artificial intelligence and computing science, among others.
In a similar sense, feedback can describe the process by which an individual receives acoustic information about the environment, information which is used for orientation with respect to it. Lack of acoustic feedback (in the sense of reflected sound) as experienced in an ANECHOIC CHAMBER may explain reactions of fear and disorientation that are reported.
See: COMMUNICATION, ECHOLOCATION, HI-FI, LO-FI, SONAR.
In TAPE MUSIC, tape feedback refers to a technique where the output of the playback head of a tape recorder is connected in the same circuit as the input to the recording head. A multiple ECHO is produced, provided there is a delay between the two heads, as there is on a machine where the heads are separate. When there is no delay, an effect similar to ACOUSTIC FEEDBACK is produced. Digital delay units allow the output signal to be recirculated into the input to produce a similar kind of feedback or multiple echo.
Compare: SOUND-ON-SOUND, TAPE ECHO, TAPE LOOP.
Sound Example: B.C. ferry horns with 0.25 sec. feedback delay creating multiple echoes.