Noise cancelling means noise or noise suppression. On the one hand, there is classic noise cancellation, which works with frequency boosts and cuts, known as emphasis, and on the other hand, interference methods, in which signals in phase opposition compensate for the noise signals because they cancel each other out.
In interference techniques, the noise signal is filtered out, rotated 180° in polarity, and superimposed on the original noise signal. The interference of both signals compensates the noise and affects the sound quality to a much lesser extent. Interference methods are active noise cancellation, Active Noise Cancelling( ANC) or Active Noise Control (ANC).
A distinction is made between Adaptive Feedback System and Adaptive Feedforward System. Whereas in the Adaptive Feedback System the noise is picked up and compensated with the sound source signal in a compensation circuit, in the Adaptive Feedforward System the sound sourcesignal is picked up directly at the sound source with a reference microphone, filtered and mixed as a control signal with the noise-affected sound signal. The filter function is controlled by a control algorithm that compares the sound source signal with the mixed sound signal.
The ANC process is mainly used in headphones.