Insertion loss testing of active noise reduction headsets using acoustic fixture

Active Noise Reduction (ANR) technique has been available for hearing protectors and communication headsets for years. However, no standard testing method for ANR headsets has emerged. In this study, we measured insertion losses of four types of commercially available ANR headsets using an Acoustic Test Fixture (ATF) to examine the feasibility of using ATF for this kind of measurement. The measurement outlined required a minimum of instrumentation and was relatively simple to implement. The results show that this method should be especially useful for testing of prototypes and for quality control as well.     

一种数字有源降噪耳机控制器设计方法

为了得到一种作用于低频宽带噪声的有源降噪耳机,采用固定系数的数字控制器实施降噪,并提出了一种前反馈混合的控制器设计方法。比较了前馈及混合两种控制模式下对低频宽带噪声的控制效果;进一步提出了一种综合优化方法,改善噪声不同角度入射下的降噪性能。仿真和基于DSP平台的实验表明,提出的方法对多方向入射的20～1500 Hz低频宽带噪声均具有较好控制效果。     

Hybrid feedforward-feedback active noise reduction for hearing protection and communication

A hybrid active noise reduction (ANR) architecture is presented and validated for a circumaural earcup and a communication earplug. The hybrid system combines source-independent feedback ANR with a Lyapunov-tuned leaky LMS filter (LyLMS) improving gain stability margins over feedforward ANR alone. In flat plate testing, the earcup demonstrates an overall C-weighted total noise reduction of 40 dB and 30-32 dB, respectively, for 50-800 Hz sum-of-tones noise and for aircraft or helicopter cockpit noise, improving low frequency (<100 Hz) performance by up to 15 dB over either control component acting individually. For the earplug, a filtered-X implementation of the LyLMS accommodates its nonconstant cancellation path gain. A fast time-domain identification method provides a high-fidelity, computationally efficient, infinite impulse response cancellation path model, which is used for both the filtered-X implementation and communication feedthrough. Insertion loss measurements made with a manikin show overall C-weighted total noise reduction provided by the ANR earplug of 46-48 dB for sum-of-tones 80-2000 Hz and 40-41 dB from 63 to 3000 Hz for UH-60 helicopter noise, with negligible degradation in attenuation during speech communication. For both hearing protectors, a stability metric improves by a factor of 2 to several orders of magnitude through hybrid ANR.     

Subspace algorithms for noise reduction in cochlear implants

A single-channel algorithm is proposed for noise reduction in cochlear implants. The proposed algorithm is based on subspace principles and projects the noisy speech vector onto "signal" and "noise" subspaces. An estimate of the clean signal is made by retaining only the components in the signal subspace. The performance of the subspace reduction algorithm is evaluated using 14 subjects wearing the Clarion device. Results indicated that the subspace algorithm produced significant improvements in sentence recognition scores compared to the subjects' daily strategy, at least in stationary noise. Further work is needed to extend the subspace algorithm to nonstationary noise environments.     

无次级通道建模有源噪声控制算法的实验研究

以管道中有源噪声控制为实验平台,基于ADSP21161N数字信号处理评估板实现了本文作者早先提出的不需要次级通道建模的基于LMS方法的四方向搜索型有源控制算法,并给出了该算法在实际应用中收敛系数的选取原则。针对单频和多频噪声的实验结果表明,前人两方向搜索型有源控制算法在大部分频率上都能收敛,但在次级通道相位为±90°的频率不能收敛,而本文作者所提出的四方向变收敛系数搜索型算法,在所有频率都能快速收敛。     

A normalized data-reusing least-mean-square algorithm of noise cancellation for magnetocardiography

An adaptive filter based on Data-Reusing Least-Mean-Square algorithm has been proposed and applied in magnetocardiography (MCG) to suppress ambient noise, Numerical simulation studies indicate that the adaptive filter is a powerful noise suppresser for correlated interferences, especially for those with amplitude changing and time delay.Also the filter has a wide frequency bandwidth. With this filter, the signal-to-noise ratio of an MCG is improved to the intrinsic noise level, The periodic average method for further improvement of the noise level in MCG is also discussed.     

调节水床效应的双梯度有源噪声控制自适应算法*

为了使自适应反馈有源噪声控制系统能够兼顾水床效应,通过约束次级信号的能量以调节噪声放大,设计了一种双梯度算法。当次级信号满足约束,算法沿着最小化误差信号能量的梯度方向迭代,反之,则沿着最小化次级信号能量的方向迭代。在有源降噪耳机实例中的对比结果表明,该算法能调节噪声放大并保持较大的降噪带宽,且运算量没有显著增加。     

Performance of personal active noise reduction devices

This paper presents the results of objective tests performed on 13 personal active noise reduction devices (earmuffs, headphones, headsets and insert earphones) divided into four groups based mainly on structure, using an acoustic test fixture (ATF). Each device was examined on its attenuation of broadband noise, overload response, internally generated noise, attenuation of impulse noise, and stability to movement. The results show a large range of responses between devices in terms of attenuation and overload, and highlight distinctive differences between the device groupings.     

A comparative intelligibility study of single-microphone noise reduction algorithms

The evaluation of intelligibility of noise reduction algorithms is reported. IEEE sentences and consonants were corrupted by four types of noise including babble, car, street and train at two signal-to-noise ratio levels (0 and 5 dB), and then processed by eight speech enhancement methods encompassing four classes of algorithms: spectral subtractive, sub-space, statistical model based and Wiener-type algorithms. The enhanced speech was presented to normal-hearing listeners for identification. With the exception of a single noise condition, no algorithm produced significant improvements in speech intelligibility. Information transmission analysis of the consonant confusion matrices indicated that no algorithm improved significantly the place feature score, significantly, which is critically important for speech recognition. The algorithms which were found in previous studies to perform the best in terms of overall quality, were not the same algorithms that performed the best in terms of speech intelligibility. The subspace algorithm, for instance, was previously found to perform the worst in terms of overall quality, but performed well in the present study in terms of preserving speech intelligibility. Overall, the analysis of consonant confusion matrices suggests that in order for noise reduction algorithms to improve speech intelligibility, they need to improve the place and manner feature scores.     

虚拟传声器在有源抗噪声护听器的应用

考察了虚拟传声器应用于有源抗噪声护听器的稳定性和降噪性能。理论上分析了虚拟传声器算法的稳定性,并通过引入反馈控制器和设计次级通道模型使得算法在不同护听器佩戴方式下都保持稳定,获得高噪声衰减和高稳定性。实验结果证实了虚拟传声器的应用可以在耳道口获得更高的窄带噪声衰减,而且所采取的措施可以保证护听器在不同佩戴状态下都能稳定。     

Improvement of noise reduction performance for a high-speed elevator using modified active noise control

A high rise building demands a high-speed elevator. Since a high-speed elevator has various transfer paths of noise transmitted from motor and rope to cabin interior, it is very difficult to solve the noise problem. Most research for noise reduction has been performed regarding passive noise control by using mainly absorption material and insulation material. In this study, while it is modeling as multiple-input and single-output with respect to transfer paths of high-speed elevator on conditions of stationary and driving states, the characterized frequency in the cabin is discovered through a contribution technique. It is able to replace by 1-dimensional model to control noise at a major contributed frequency. Also, a new active noise control technique has been proposed to control the cabin noise effectively at unpleasant area that is required to make quite zone for passenger. The Correlation Filtered X-LMS (Co-FXLMS) algorithm has been applied to control the dominant frequency noise that it has a high contribution. Simultaneously, this study has a proposed Moving Band Pass Filter (MBPF) to improve the performance of active noise control in the cabin which is able to apply a dynamic system with time variant states. Finally, we obtained the 8 dB noise reduction in the cabin at ear level and it has been proved that the modified active noise control using Co-FXLMS algorithm and MBPF is available to improve the performance of noise reduction.     

空间有源消声实验研究

本文分别在半声室和普通房间进行有源消声实验，证明了作者以前提出的算法是收敛的，稳定的，以此算法构成的多通道有源消声系统对直达声和混响声都能进行了有效的控制。     

空间有源消声的声能量流研究

本文从理论和实验两个方面对平面噪声场中单极子次级源、偶极子次级源最小辐射声功率时的空间产能量流作了研究,从而直观、清晰地描述了一种消声机理:有源声吸收。并指出:尽管此时次级声源是\     

An active noise reduction earplug using a piezoelectric laterally radiating loudspeaker

This paper describes the electroacoustic behaviour of a new piezoelectric Active Noise Reduction (ANR) earplug device. The sensor is a microphone having suitable characteristics chosen from among commercially available electret microphones. The actuator is a cylindrical piezoelectric ceramic loaded with a thin fluid film. An analytic model of laterally radiating loudspeaker, based on fundamental equations of acoustics, which takes into account the effect of viscosity and heat conduction is adapted to describe the acoustic radiation of the actuator. Theoretical and experimental frequency responses in a small cavity and an example of the ANR that can be obtained with the earplug are presented.     

皮层脑电的非线性降噪

引入基于对非线性动力学局部线性拟合的局部投影非线性降噪方法对Spragure-Dawley大鼠的皮层脑电进行降噪.为了提高降噪效果，利用返回图法对皮层脑电降噪时所需要的最佳局部邻域尺度进行了估计.首先以被50%的高斯白噪声污染的Lorenz方程x轴为例进行降噪，说明根据降噪理论所编写的计算程序的正确性.然后将此降噪方法分别应用于被麻醉的大鼠的皮层脑电和青霉素溶液诱发癫痫发作的皮层脑电时间序列，并采用非线性预报分析说明降噪的效果. 关键词： 皮层脑电 返回图法 非线性降噪 非线性预报     

Nonlinear noise reduction for electrocardiograms

The electrical activity of the heart usually shows dynamical behavior which is neither periodic nor deterministically chaotic: The interbeat intervals seem to contain a random component. Although long term predictions are thus impossible, good predictions can be made for times smaller than one heart cycle. This fact is used in order to suppress measurement errors by a local geometric projection method which was originally developed for chaotic signals. The result constitutes evidence that techniques of time series analysis based on chaos theory can be useful despite the fact that very few natural phenomena have been actually established to be deterministically chaotic. (c) 1996 American Institute of Physics.     

An experimental evaluation of noise reduction by scattering in low velocity ducts

This paper presents the results of an experimental assessment of both conventional absorption and Bragg scattering techniques for the reduction of noise transmission by a fan in a short, low velocity duct connecting two reverberant rooms. There are several advantages of using the scattering technique; for example, the saving of space and the facts that the device can be tuned to a particular frequency and that it is not necessary to use materials such as absorbent foams which can be a health hazard. The system appears to work equally well with externally generated sources of sound but the maximum attenuation with eight scatterers is found to be about 12 dB at the Bragg frequency.     

Design and experimental tests of active control barriers for low-frequency stationary noise reduction in urban outdoor environment

Active noise control (ANC) techniques are based on the emission of an antiphase signal in order to cancel the noise produced by a primary source. ANC has been successfully applied especially for reducing noise in confined environments, such as headphones and ducts. In this study, we present an application of ANC concepts to the design of an anti-noise barrier for an outdoor environment and its experimental testing. Even though passive techniques are effective in noise reduction at middle-high frequencies, they become less efficient at low frequencies (below 300 Hz) due to the limited dimensions of commonly deployable barriers. In this paper, we analyze the properties of a low-cost active noise system able to efficiently operate on stationary, almost pure-tone, low-frequency noise, such as that produced by electrical transformers and reactors in power and transformation plants. A prototype has been implemented and on-the-field experimental tests have been carried out. The results (confirmed also by numerical simulations) demonstrate a remarkable efficiency in the far field, with a reduction up to 15 dB with respect to the absence of the ANC system.