A robust narrowband active noise control system for accommodating frequency mismatch

Narrowband active noise control (ANC) systems have many real-life applications where the noise signals generated by rotating machines are modeled as sinusoidal signals in additive noise. However, when the timing signal sensor, such as a tachometer that is used to extract the signal frequencies, and the cosine wave generator contain errors, the reference signal frequencies fed to each ANC channel will then be different from the noise signal true frequencies. This difference is referred to as frequency mismatch (FM). In this paper, through extensive simulations we demonstrate that the performance capabilities of a conventional narrowband ANC system using the filtered-X LMS (FXLMS) algorithm degrades significantly even for an FM as small as 1%. Next, we propose a new narrowband ANC system that will successfully compensate for the performance degradations due to FM. The amplitude/phase adjustment and the FM mitigations are performed simultaneously in a harmonic fashion such that the influence of the FM can be removed almost completely. Simulation results are provided to demonstrate the effectiveness of the proposed new system.