Noise reduction using FeedForward ANC System based on online secondary path modeling

Destructive interference is the principle on which ANC (active noise control) system is based. In destructive interference an anti-noise signal is generated using adaptive filter and is superimposed upon noise signal, as a result the unwanted noise is reduced. The secondary path of ANC is assessed off-line prior to use of ANC system when no reference noise exists. But, in practical applications, reference noise exists and secondary path may be varying with time. This may lead to ANC system instability and adaptive filter may not be able to converge. In such cases, this time varying secondary path should be modeled online to make sure proper functioning of ANC system. In this paper, ANC system based on online modeling of secondary path is applied to ambulance siren noise. The simulations performed in MATLAB show that noise level is reduced by approximately 37 dB, which is a considerable reduction in noise level.