Active noise control algorithms with reduced channel count and their stability analysis

In narrowband active noise control systems, the dimension of the quiet zone around each error sensor is proportional to the wavelength of the noise being cancelled. In broadband active noise control systems, several error sensors per anti-noise source are used (two as a rule of thumb) in order to achieve larger cancellation regions, but the fact still remains that the size of the quiet zone will be proportional to the wavelength of the noise. In this paper, it is proposed to achieve wide quiet zones by bandlimiting the anti-noise signal. This results in techniques that do not need the extra number of error sensors. This cannot be done by placing a filter in the cancellation path, or using the anti-aliasing or reconstruction filters, unless you use a very sharp filter with long delay. Instead, several algorithms based on the MFxLMS algorithm are presented that accomplish this task. This permits systems with more anti-noise sources than error sensors, which allows a better inversion of the cancellation path while still achieving large quiet zones. The new algorithms are less sensitive to cancellation path modelling errors. Namely, the maximum error allowed in the delay estimate increases as the anti-noise bandlimiting frequency decreases.