Audio feedback

Audio feedback is a sustained or escalating sound produced when amplified sound re-enters its input path. It occurs when the loop reinforces particular frequencies strongly enough to overcome losses.

Feedback loop: A process in which part of a system’s output returns as input and affects later output. The microphone, amplifier, and loudspeaker form a loop when sound returns to the microphone.
Public address system: An electronic system that amplifies speech or other sound for an audience. Its nearby microphones and loudspeakers make acoustic feedback a common operating problem.
Audio distortion: A change to an audio signal that alters its waveform or perceived sound from the input. Feedback is one source of distortion, but its defining feature is a returning signal that sustains itself.
Gain before feedback: The maximum amplification a sound system can provide before acoustic feedback begins. It quantifies the practical limit feedback places on a microphone and loudspeaker system.
Acoustic coupling: Transfer of sound between devices or spaces through the air or another medium. Sound from the loudspeaker reaches the microphone and closes the acoustic path.
Microphone: A transducer that converts sound waves into an electrical signal. Microphone placement and direction strongly affect how much amplified sound returns to the input.
Clipping (audio): A form of distortion caused when an audio signal exceeds a system’s available amplitude range. Clipping comes from amplitude limits, not sound looping from output back into input.
Feedback (music): The use of sound feedback as a musical texture, gesture, or source of sustained tones. Musicians turned an unwanted amplification artifact into a controllable sound material.
Loop gain: The total amplification or attenuation experienced by a signal during one traversal of a feedback loop. Feedback grows when loop gain exceeds unity at a frequency whose phase also supports reinforcement.
Loudspeaker: A transducer that converts an electrical audio signal into sound waves. Its output can recirculate through the room and enter a microphone.

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