Saturation effects in active noise control systems

The reference and error sensors of active noise control (ANC) systems will be saturated in real-world applications if the noise level exceeds the dynamic range of the sensors. However, there is a lack of analysis of saturation effects on the performance of ANC systems. This paper proposes an indirect method for analyzing the saturation effects in steady state using Fourier analysis. This indirect method uses clipping to approximate saturation and decomposes the saturated narrowband signal as the summation of a set of rectangular waves and a pulse-amplitude modulated signal. The theoretical analysis shows that the clipping of a sinusoidal signal produces extra odd harmonics, thus affecting the convergence speed and steady-state solution of adaptive filter in ANC systems. This analysis can be extended to narrowband noises that consist of multiple sinusoidal components such as engine noise in many ANC applications. A low-pass filter is effective in reducing saturation effects for harmonic-related noises. Analysis results are verified by computer simulations using recorded engine noise and transfer functions measured from an experimental setup.