Noise cancellation, also called as Active noise control is a technique, in which unwanted ambient sounds are reduced by an addition of a cancelling sound. Sound has wave nature and is created when a vibrating body influences its medium to vibrate. This wave is consists of areas with high and low pressures, also called as compressions and rarefactions respectively. The varying pressure has different frequencies and amplitudes. The varying pressure has different frequencies and amplitudes, which is the extent of the pressure. Waves with greater amplitude are louder while a wave with a low frequency would have a higher pitch.
Noise cancellation should not be confused with sound proofing which involves completely blocking unwanted noise. Let’s refer to a single wave of sound which is sinusoidal in nature. The wave has certain amplitude “a.” When a similar wave with same their troughs and peaks aligned, is superimposed onto this wave, the amplitude doubles. Similarly, when two opposite waves are superimposed with the troughs aligned with the peaks and vice versa, they both cancel each other out ant there is no sound. When two waves are imposed on each other the phenomenon is called interference. In the first scenario when the waves added up to deliver greater amplitude, it is called as constructive interference, while the cancelling or reduction of amplitudes due to interference is called as destructive interference.
In noise cancellation, we use destructive interference. An input device records the sound waves that consist of desired an undesired sounds (noise). Once the noise waves are identified, inverse phase waves, meaning opposing waves are set out to interfere with the noise waves. This leads to both waves cancelling each other out and the user now only hears the desired sounds.
Repeating and predictive sounds are easier to cancel out over random and active sounds from the surroundings. Noise cancellation is a technology widely used in aviation and professional gaming.