Acoustic noise and echo cancelling with microphone array

A novel method of performing acoustic echo cancelling using microphone arrays is presented. The method employs a digital self-calibrating microphone system. The calibration process is a simple indirect on-site calibration that adapts to the particulars of the acoustic environment and the electronic equipment in use. Primarily intended for handsfree telephones in automobiles, the method simultaneously suppresses the handsfree loudspeaker and car noise. The system also continuously takes into account disturbances such as fan noise. Examples from an extensive evaluation in a car are also included. Typical performance results demonstrate 20-dB echo cancellation and 10-dB noise reduction simultaneously     

Robust broadband beamformer design for noise reduction and dereverberation

Multidimensional Systems and Signal Processing - In this paper, we investigate robust design methods for broadband beamformers in reverberant environments. In the design formulation room...     

Optimization of a cascaded structure for noise and echo cancellation using a noise filtering preprocessing

This paper deals with speech enhancement in hands-free telecommunication systems. The two major problems encountered in such contexts - noise reduction and acoustic echo cancellation - are addressed. After the presentation of the two basic cascaded structures found in the literature, we propose a new promising technique which takes advantage of the previous ones. The main objective is to get a near-end speech signal with low levels of distortion, echo and noise. The structure is tested in a real mobile environment and compared with the two others. An objective evaluation shows the improvement provided by this structure.     

Active cancellation of acoustic noise using a self-tuned filter

In an increasingly noisy society, methods of reducing noise are becoming more important. This work proposes an analog electroacoustic circuit for active control of narrow-band low-frequency acoustic noise using adaptive filtering techniques. The circuit aims at producing antinoise, which is acoustically added to the disturbing noise to produce an error signal that is fed back to the circuit. The proposed circuit is a modified Kerwin-Huelsman-Newcomb biquad filter that tunes itself to the incoming noise frequency using the zero tuning techniques. The circuit was implemented on a printed circuit board and it was successful in reducing noise by 15-20 dB in open space. Active noise control specifically for narrow-band noise cancellation using adaptive analog filters seems to be a better solution than its digital signal processing counterpart in speed, cost, and robustness.     

CAD of signal processing architectures: an application to acoustic echo cancellation

The integration capabilities ofvlsi technology allow for implementation of complex real time applications of signal processing. Whether these circuits are dedicated(asics) or programmed (processors and multiprocessors), it is necessary to use adequate methods andcad tools which aid the design of complex systems and circuits. These will then make it possible to implement real time applications with a reduced cost of development and production. Today these methods give interesting results, both for the design of multiprocessor systems, as well as forasics. They are based on a formalism for the modeling of algorithms and architectures, and on optimization techniques for the design. We present the basic characteristics of these methods. We show some results in acoustic echo cancellation in the area of multiprocessors and in the field ofasics.     

Adaptive filtering in subbands with critical sampling: analysis,experiments, and application to acoustic echo cancellation

An exact analysis of the critically subsampled two-band modelization scheme is given, and it is demonstrated that adaptive cross-filters between the subbands are necessary for modelization with small output errors. It is shown that perfect reconstruction filter banks can yield exact modelization. These results are extended to the critically subsampled multiband schemes, and important computational savings are seen to be achieved by using good quality filter banks. The problem of adaptive identification in critically subsampled subbands is considered and an appropriate adaptation algorithm is derived. The authors give a detailed analysis of the computational complexity of all the discussed schemes, and experimentally verify the theoretical results that are obtained. The adaptive behavior of the subband schemes that were tested is discussed     

一种新NLMS自适应滤波算法及其在多路回波消除中的应用

提出一种NLMS改进算法并对其收敛性进行了证明。该算法计算复杂度低于Sankaran(1997)所提出的带有正交改正因子的归一化算法(NLMS-OCF)和仿射投影算法(APA),并具有易于实现等特点。仿真结果表明,以单路语音信号作输入时,新算法具有比NLMS-OCF算法更好的收敛速度和精度,而在收敛速度和精度相当的情况下,新算法比APA算法所占用的CPU时间少。将新算法扩展成两路算法后,扩展算法仍然保持了这些特点,与Sankaran(1999)两路NLMS-OCF及Benesty(1996)所提多路仿射算法(APA-MC)相比,新算法更适合于应用到多路回波消除等实时性要求高的场合。1     

Comparison of pole-zero and all-zero modelling of acoustic transfer functions (echo cancellation)

Echo cancellation in teleconferencing systems or loud-speaking telephones requires the modelling of acoustic transfer functions of rooms. It might he expected that for reverberant acoustical situations a pole-zero representation would be much more economical than an all-zero one. It is shown that this is not the case.<>     

Cascaded power symmetric IIR filter banks and continuityconstrained adaptive algorithms for acoustic echo cancellation insubbands

Teleconferencing systems and hands-free mobile terminals use acoustic echo cancellation (AEC) for high-quality full-duplex speech communication. The problem of aliasing in subband AEC is addressed. Filter banks with implicit notch filtering are derived from cascaded power symmetric-infinite impulse response (CFS-IIR) filters. It is shown that adaptive filters used with these filter banks must be coupled via continuity constraints to reduce the aliasing in the residual echo. A continuity constrained NLMS algorithm is therefore proposed and evaluated     

SVD-based optimal filtering for noise reduction in dual microphone hearing aids: a real time implementation and perceptual evaluation

In this paper, the first real-time implementation and perceptual evaluation of a singular value decomposition (SVD)-based optimal filtering technique for noise reduction in a dual microphone behind-the-ear (BTE) hearing aid is presented. This evaluation was carried out for a speech weighted noise and multitalker babble, for single and multiple jammer sound source scenarios. Two basic microphone configurations in the hearing aid were used. The SVD-based optimal filtering technique was compared against an adaptive beamformer, which is known to give significant improvements in speech intelligibility in noisy environment. The optimal filtering technique works without assumptions about a speaker position, unlike the two-stage adaptive beamformer. However this strategy needs a robust voice activity detector (VAD). A method to improve the performance of the VAD was presented and evaluated physically. By connecting the VAD to the output of the noise reduction algorithms, a good discrimination between the speech-and-noise periods and the noise-only periods of the signals was obtained. The perceptual experiments demonstrated that the SVD-based optimal filtering technique could perform as well as the adaptive beamformer in a single noise source scenario, i.e., the ideal scenario for the latter technique, and could outperform the adaptive beamformer in multiple noise source scenarios.     

Hybrid excitation of SRM for reduction of vibration and acoustic noise

The inherent simplicity, ruggedness, and low cost of a switched reluctance motor (SRM) makes it a viable candidate for various general-purpose adjustable-speed applications such as industrial and home appliances. The primary disadvantage of an SRM is the vibration and acoustic noise compared with that of conventional machines. The main source of vibration in the SR drive is generated by rapid change of radial magnetic force when phase current is extinguished during commutation action. In this paper, a hybrid excitation method with C-dump inverter is proposed to reduce vibration and acoustic noise in the SR drive. The hybrid excitation has two-phase excitation by long dwell angle as well as conventional one-phase excitation. The vibration and acoustic noise are reduced because the scheme reduces abrupt change of excitation level by distributed and balanced excitation.     

Phase noise and a low-frequency noise reduction method in bipolartransistors

A low-frequency amplitude and phase-noise measuring system was set up and both noises were measured. It is noted they were correlated in a bipolar transistor. Both noises were from the same origin: diffusion coefficient fluctuation in the base. A demonstration was carried out on the amplitude noise reduction by using the correlation between both noises     

Systematic analysis and cancellation of kickback noise in a dynamic latched comparator

A dynamic latched comparator can suffer from three non-idealities: offset voltage, random noise and kickback noise. Specifically in an analog-to-digital converter (ADC) the kickback noise of a comparator can noticeably affect the settling time and accuracy of the decision. This work offers an analytical treatment of kickback noise generation, and proposes a synchronized kickback noise cancellation technique, which is achieved via placing clocked NMOS-PMOS capacitors at the proper nodes to cancel out effectively those unwanted charges (electrons or holes) under different operating regions of the MOS devices. The technique is clock-rate insensitive and particularly suitable for the SAR-type ADC as it will not alter the charge stored in the capacitor array. Optimized in 65-nm CMOS the kickback noise is <±0.3 mV in 30× Monte–Carlo simulations at both 50- and 500-MHz clock rates. For 10-bit resolution in a full scale of 1 V_pp, the kickback noise of the proposed comparator comparing with the conventional one is improved by 48×, from 6.27 to 0.13 LSB.     

Three-stage adaptive noise cancellation for arbitrary signals using a source-embedded pilot signal: Method 2

Two-stage noise cancellation is a recently introduced technique for cancelling noise while maintaining minimal signal distortion due to signal leakage into the noise reference. An alternative three-stage approach to noise cancellation that extends applicability from intermittent or slowly fluctuating signals to arbitrary signals is presented. This alternative is viable whenever the signal source is accessible so that a pilot signal can be additively embedded.     

High-frequency FET noise performance: a new approach

A formulation is proposed for calculating the FET noise performance in the high-frequency range (EHF). In the first step, the concept of a local small-signal equivalent circuit is introduced, and a novel method for calculating the FET admittance parameters is proposed. In the second step, a novel formulation of the impedance field is given. It is shown that this approach reflects better the frequency evolution of the noise source values and consequently gives a better noise figure     

Performance evaluation of acoustic echo control: required values and measurement procedures

We consider in this paper the general problem of performance evaluation of acoustic echo control, and (with less emphasis) of speech enhancement, as basic functions to be integrated in terminals like hands-free telephones, videophones, teleconference systems, etc, globally named hands-free audio terminals. Performance requirements are first reviewed under the light of desirable correspondence between objective characteristics and subjective quality. Some typical examples illustrate the discussion. Then the problem of performance verification is considered, with emphasis on test signals. Outlines for future directions of research on the topic of performance evaluation and verification are finally sketched.     

High-efficiency and low acoustic noise drive system using open-winding AC motor and two space-vector-modulated inverters

The combining of the outputs of two inverters using interphase reactors is a widely used method for supplying large AC drives rated at more than several thousands kilowatts. Certain drawbacks are associated with this method, such as high acoustic noise and high losses due to the interphase reactors. To overcome these problems, the authors propose a new high-efficiency drive system using an open-winding motor and two space-vector-modulated inverters. This configuration consists of a three-level inverter with switching at once every cycle and a two-level inverter of about 1-kHz switching frequency, connected, respectively, to the opposite terminals of the open-winding AC motor. With the proposed configuration, good current waveforms, high efficiency, and low acoustic noise can be obtained.     

Three-stage adaptive noise cancellation for arbitrary signals using a source embedded pilot signal: Method 1

Two-stage noise cancellation is a recently introduced technique for cancelling noise while maintaining minimal signal distortion due to signal leakage into the noise reference. An alternative three-stage approach to noise cancellation that extends applicability from intermittent or slowly fluctuating signals to arbitrary signals is presented. This alternative is viable whenever the signal source is accessible so that a pilot signal can be additively embedded.