Feedback is a condition where the output of a circuit recycles through its input. Acoustic feedback is a loud squeal or whine that occurs in live audio situations when an amplified sound re-enters a sound system through the same microphone (or guitar pickup) that reproduced the original source, creating a loop. The particular sound heard is a result of the resonance characteristics of the circuit and the acoustic environment. Feedback also can be used in signal processing; for example, part of a signal routed through a digital delay can be fed back into the delay to create a more complex effect. This is also known as regeneration.