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Abstract

An active noise control (ANC) system is disclosed for attenuating engine generated noise that contains at least one sinusoidal noise component having an amplitude and frequency that vary with changes in engine rotational speed. The ANC system includes a means for generating an input signal that contains one or more sinusoidal signal components, where each signal component has a frequency corresponding to that of a respective one of the noise components. The input signal is filtered with an adaptive filter having adjustable filtering characteristics to produce a filter output signal. Noise canceling waves are generated by a noise canceling actuator in response to the filter output signal, and the canceling waves are superimposed with the undesirable noise generated by the engine. The level of residual noise resulting from this superposition is sensed and a corresponding error signal is developed. The filtering characteristics of the adaptive filter are adaptively adjusted in accordance with the error signal and sensed indications for the engine rotational speed and acceleration. In the preferred embodiment, the characteristics of the adaptive filter are adjusted according to an algorithm having a convergence factor and a leakage factor, where the value of the convergence factor is scaled as a function of engine acceleration and the value of the leakage factor is scaled as a function of engine speed and acceleration.

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