On maximum achievable noise reduction in ANC systems

Active noise control (ANC) is primarily a signal estimation problem. The nature of noise to be canceled, the acoustic paths, and the transfer functions of microphones/loudspeakers place fundamental limits on the performance of ANC systems. In this paper we analyze the performance of ANC systems from the maximum achievable noise attenuation level (NAL_max) prospective for different ANC system structures i.e feed-forward, feedback and hybrid. We first derive NAL_max for stochastic noise and then generalize the result to accommodate tonal (sinusoidal) noises. These results are invaluable in choosing an ANC design scheme.