Active noise control

Active noise control (ANC) (also known as noise cancellation, active noise reduction (ANR) or antinoise) is a method for reducing unwanted sound by using a polarity inducing noise signal to cancel it. An example would be a pair of "noise canceling" headphones that implement the technique by using a small microphone to receive the noise outside the headphones, invert it and then add it back to the headphone signal. This partially reduces the noise level heard inside the headphones.