Adaptation in active noise control — A simulation case study

Accurate model of secondary paths is very crucial for the multi-channel filtered-X least mean square algorithm applied in adaptive active noise control system. The auxiliary random noise technique is popular for online secondary path modeling during adaptive active noise control operation. This paper proposes a simplified variable step-size strategy and an effective auxiliary noise power scheduling strategy for the multi-channel filtered-X least mean square algorithm. Through a defined indirect error signal, the proposed method can guarantee every online secondary path modeling filter has its own exclusive variable step-size strategy to update their coefficients, and every injected noise has its own exclusive scheduling strategy considering all of the corresponding online secondary path modeling filters. The proposed method can improve the adaptive performance and simplifies the complexity of multi-channel adaptive active noise control system. Computer simulations show that the proposed method gives much better noise reduction and secondary path modeling accuracy at a somewhat faster convergence rate comparing with the competing methods.

Based on the analysis of the characteristics of practical noises in a driver's cab, and aiming at the real time signal processing requirements, the high speed digital signal processor is used in the active noise control system. And combined with the nonlinear characteristics of the noise, an adaptive active noise control project based on the radial basis function neural network is proposed, at the same time an filter algorithm is given. The result proves the proposed adaptive active noise control system to be feasible and effective.

A feedforward active noise control (ANC) system requires a reference signal correlated with the primary disturbance. In situations when such correlated reference signal cannot be obtained, a feedback type ANC may be employed. A hybrid ANC system is combination of feedforward and feedback control, where objective is to simultaneously control both the correlated and uncorrelated primary disturbances. In this paper, we identify problems with the conventional hybrid ANC systems, and propose an improved performance hybrid ANC system. The proposed method introduces third adaptive filter to the conventional hybrid ANC system. The objective is to generate appropriate error and reference signals for feedforward and feedback ANC filters. Computer simulations are carried out which demonstrate that the proposed method can effectively mitigate the correlated and uncorrelated primary disturbances appearing at the error microphone.

This paper presents the feed-forward multichannel active noise control which was simulated on LabVIEW and experimented on two channel feed-forward active noise control in real-time. The simulation of feed-forward multichannel active noise control system was built on LabVIEW by using FxLMS algorithm and other algorithms such as Variable Step-size (VSS) and saturation compensation. Moreover, LMS and VSS LMS algorithm were used to train the secondary path in order to improve the convergence speed and stabilization of ANC system in the real-time. The experimental results show that the ANC system in real-time using variable step-size and without using variable step-size algorithm work effectively with noise sources which were synthesized from one to three frequencies. The noise level in these cases decreased around 12 dB - 35 dB and the noise reduction radius measured is about 3 cm around the microphone.

This paper analyzes a narrowband feedforward active noise control (ANC) system using internally synthesized sinusoid as the reference signal. The effect of frequency error between the primary noise and the reference signal on the performance of the ANC system is evaluated in terms of noise reduction in steady state. Theoretical analysis shows that the achievable noise reduction is decreased for increased frequency error, but can be improved by using larger step size. These theoretical results are verified by computer simulations of the narrowband ANC system with transfer functions measured from a real experimental setup.

A modified feedforward hybrid active noise control system for vehicle

Based on the theoretical analysis of literature, saturation in measured signal of active noise control (ANC) systems will degrade the convergence speed. However, the experiments show that the saturated input signal can speed up the convergence of the narrow-band ANC systems. This paper intends to remodel the saturation effects for feedforward and feedback ANC systems. Combining the action of analog-to-digital converters (ADC), the mathematical expression and block diagrams are proposed to model the saturation effects in the practical ANC systems. The derivation and simulation results show that since the saturation is able to amplify the principle component of signal, the convergence would be speeded up.

Stochastic analysis of FXLMS-based internal model control feedback active noise control systems

Multichannel feedforward active noise control system combined with noise source separation by microphone arrays

This research developed active noise control (ANC) system for in-ear headphones based on the feedforward algorithm to reduce broadband noise. The setup of the designed ANC in-ear headphones contains a microphone that receives external noise and a digital signal processor as the computing core to generate the anti-noise. This research analyzed the noise attenuation performance of the feedforward ANC system with noise from different direction-of-arrival (DOA). Finally, the experimental results showed that the attenuation performance of the feedforward controller depends on the DOA of the noise. Moreover, we compared the proposed in-ear headphones with commercially available ones to verify their effectiveness in an anechoic chamber.

In filtered-x LMS (FxLMS) single-channel feedforward active noise control (ANC) systems, a reference signal is available that is correlated with the primary disturbance at the error microphone. In some practical situations, there may also be a disturbance uncorrelated with the primary disturbance at the error microphone, for which a correlated reference signal is not available. This disturbance, being uncorrelated with the primary noise, cannot be controlled by the standard FxLMS algorithm, and increases the residual noise. In this paper we propose an improved hybrid ANC system that can simultaneously control both the correlated and uncorrelated noise signals. The proposed method comprises three adaptive filters: 1) the FxLMS-based ANC filter to cancel the primary noise; 2) a separate FxLMS-based ANC filter to cancel the uncorrelated disturbance; and 3) an LMS-based supporting adaptive filter to generate appropriate signals for the two ANC filters. Computer simulations demonstrate that the proposed method can effectively mitigate the correlated and uncorrelated primary disturbances. This improved performance is achieved at only a small increase in computational complexity.

All-pass filtered x least mean square algorithm for narrowband active noise control

Integrated active noise control for open-fit hearing aids with customized filter

Cascading time-frequency domain filtered-x LMS algorithm for active control of uncorrelated disturbances

The convergence characteristics of the feedforward active noise control system with the filtered-x LMS or multiple error filtered-x LMS algorithm are degraded by the transfer functions from the secondary sources to the error sensors (secondary paths). The possible methods to improve the convergence characteristics of the active noise control system with the LMS algorithm by reducing the effect of the secondary paths are discussed in this paper. In the first method, an index in the case of multiple secondary sources and error sensors to evaluate are introduced whether their positions are good or not before performing the cancellation. In the second method in which the number of secondary sources is increased, it is shown that the LMS adaptive algorithm performs well. In the third method with the use of the inverse filters of the secondary paths, the adaptive LMS algorithm is formulated and it is shown from the result of with a simulation using a transfer function measured in a room with a reverberation time of 0.5 s that this method is practically effective.