A new narrowband active noise control system in the presence of sensor error

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 narrow-band 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 (sensor error) can be removed almost completely. Simulation results are provided to demonstrate the effectiveness of the proposed new system.

1. INTRODUCTION

In many real-life environments there may exist various unwanted sounds or noise signals that are harmful to the people working and/or living there. In many cases, the noise signals are generated by rotating ma-chines, such as engines, cutting machines, fans, etc. and may be modeled as sinusoidal signals in additive noise. Usually, the frequencies of the noise signals are unknown, and their magnitudes are time-varying. Removing or reducing these noise signals, especially the lower frequency portion, is very important in various environmental and engineering systems. For example, large-scale cutting machines used in factories generate such noise signals which are harmful to their operators. As the environmental noise level regulations are made stricter, effective measures need to be developed to reduce the noise level. Active noise control (ANC) systems have been utilized in reducing these annoying noise signals, and research in this area has been carried out since the early 1970s [1]–[5].