Double Talk Research Articles

Wavelet-Based ICA Using Maximum Likelihood Estimation and Information-Theoretic Measure for Acoustic Echo Cancellation During Double Talk Situation

Acoustic echo cancellation (AEC) plays a prominent role in the present-day hands-free communication environment, owing to the usage of adaptive digital filter techniques. In a duplex communication scenario, there is a need for a double talk detection algorithm in the near-end speaker system which disables the update of the adaptive filter coefficients, thus hindering the process of echo cancellation and leading to a partial solution. To completely solve this problem, independent component analysis (ICA) is used to separate the far-end echo from the mixture of the near-end speech and the far-end echo signal. This paper proposes a new adaptive digital filter using maximum likelihood estimation of ICA and minimization of mutual information of ICA techniques for AEC. The advancement to this technique is made by transforming the observation into an adequate representation using wavelet decomposition. The performance of the echo cancellation is measured in terms of the echo return loss enhancement (ERLE). Higher ERLE indicates better echo cancellation. From the simulation results, it is found that the minimization of the mutual information of ICA has a higher value of ERLE than that by maximum likelihood estimation. The efficiency of the system thus increases by minimizing the processing time using wavelet ICA-based adaptive filter over the conventional adaptive filter.

Donor's Double Talk Undermines African Agency - Comparative Study of Civic Agency in Burkina Faso and Togo

Despite a long-standing controversy about aid-effectiveness in general and the impact of aid-dependency on governance in particular, little is known on the effect of donors policies on civic agency for democratization in aid dependent autocratic regimes. In this study it is argued that the long-term effects of double-talk of donors, who openly promote democracy and freedom but covertly follow overriding hidden interest, are a neglected source of failure of civic protest and democratic revolutions in autocratic regimes. The differing outcome of ‘democratic revolutions’ in Togo and Burkina Faso – both ‘aid darlings’ for decades - serves to substantiate this thesis. A systematic and holistic consideration is necessary for an unbiased evaluation of the hidden adverse impact of aid on collective action at the grass-roots. Therefore, a rethinking of temporal and disciplinary ‘fault lines’ in development politics as well as in development studies is essential.

Lo que a nadie asusta pero a todos preocupa. Etnografía de los miedos cotidianos en una comunidad del altiplano sur boliviano

From the idea that fear is installed in our lives, I analyze the double talk of fears denied and concerns recognized from which the inhabitants of a community in the Bolivian high-plateau explain their daily lives, paying particular attention to the reasons given by adults in the education of children when being in certain environments or forbid them to perform certain actions. So, I will present a spatial distinction among urban settings: the own spaces, secure and recognized —but potentially threatened—, and the territory of the others , which the concurrency of past and present terrible otherness transforms in a frightening geography where things happen , fear scenarios that need to be conspirators and reordered.

주입력신호의 LPC 필터 이득을 이용한 반향제거기의 수렴전 동시통화검출 성능 개선

본 논문에서는 반향제거기가 수렴하기 전에 동작할 수 있는 기존 동시통화검출법의 성능을 개선하기 위한 방법을 제안하였다. 제안된 방법은 LPC 필터 계수를 주입력신호로부터 추정하게 된다. 동시통화검출을 위한 문턱치는 주입력신호의 크기별로 기대되는 LPC 필터 이득치를 사용하여 가변적으로 설정하게 된다. 제안한 방법은 기존의 방법이 갖고 있는 단일통화를 동시통화로 잘못 판단하는 오검출률을 개선할 수 있을 뿐만 아니라 동시통화 검출 지연 시간도 단축시킬 수 있다. 장시간의 음성신호를 사용한 모의실험을 수행하였다. 제안한 방법이 기존 방법의 오검출률을 감소시키고 동시통화 검출 지연시간을 단축시킴을 확인할 수 있었다. This paper proposes a performance improvement method of the conventional double talk detection method which can operate before convergence of the echo canceller. The proposed method estimates the coefficients of the linear predictive coding(LPC) filter by using the primary input signal. The time-varying threshold for double talk detection is determined based on the LPC filter gain of the primary input signal level. The proposed method can reduce not only false detection rate which means wrong detection of single talk as double talk but also double talk detection delay. Computer simulation was performed using a long-term real speech signals. It is shown that the proposed method improves the conventional method in terms of lowering the false detection rate and shortening the detection delay.

A Frequency-Domain Adaptive Filter (FDAF) Prediction Error Method (PEM) Framework for Double-Talk-Robust Acoustic Echo Cancellation

In this paper, we propose a new framework to tackle the double-talk (DT) problem in acoustic echo cancellation (AEC). It is based on a frequency-domain adaptive filter (FDAF) implementation of the so-called prediction error method adaptive filtering using row operations (PEM-AFROW) leading to the FDAF-PEM-AFROW algorithm. We show that FDAF-PEM-AFROW is by construction related to the best linear unbiased estimate (BLUE) of the echo path. We depart from this framework to show an improvement in performance with respect to other adaptive filters minimizing the BLUE criterion, namely the PEM-AFROW and the FDAF-NLMS with near-end signal normalization. One of the contributions is to propose the instantaneous pseudo-correlation (IPC) measure between the near-end signal and the loudspeaker signal. The IPC measure serves as an indication of the effect of a DT situation occurring during adaptation. We motivate the choice of FDAF-PEM-AFROW over PEM-AFROW and FDAF-NLMS with near-end signal normalization, based on performance, computational complexity and related IPC measure values. Moreover, we use the FDAF-PEM-AFROW framework to improve several state-of-the-art variable step-size (VSS) and variable regularization (VR) algorithms. The FDAF-PEM-AFROW versions significantly outperform the original versions in every simulation. In terms of computational complexity, the FDAF-PEM-AFROW versions are themselves about two orders of magnitude cheaper than the original versions.

Modified Approach for VSS NLMS Algorithm for Echo Cancellation in Teleconference System

communication or wireless phones have become need of everyone in this technological era of global communication. Wireless phones not only provide voice communication, they can also easily be used for other services. But voice quality is always preferable over other services of cellular networks. This demand of superior voice quality, just as like as wired line, over a wireless network has developed and is known as echo cancellation. The main aim of the acoustic echo cancellation is to remove the echoes present in desired signal and to provide echo free speech to the listeners. In this paper, a new approach for acoustic echo cancellation (1) and double talk detection for a teleconference system in non stationary environmental conditions is proposed. In this approach the impulse response of the loud speaker is assumed to be available and is estimated from the digital low pass filter. This approach is more common in the sense that it is applied to all existing algorithms. Performance evaluation of the proposed algorithm is known by calculating echo return loss enhancement (ERLE). This approach shows better performance for non stationary environment and reduces the complexity of both acoustic echo cancellation and double talk detection algorithms and this can be implemented with the help of MATLAB.

Wiener variable step size and gradient spectral variance smoothing for double-talk-robust acoustic echo cancellation and acoustic feedback cancellation

Double-talk (DT)-robust acoustic echo cancellation (AEC) and acoustic feedback cancellation (AFC) are needed in speech communication systems, e.g., in hands-free communication systems and hearing aids. In this paper, we derive a practical and computationally efficient algorithm based on the frequency-domain adaptive filter prediction error method using row operations (FDAF-PEM-AFROW) for DT-robust AEC and AFC. The proposed algorithm features two main modifications: (a) the Wiener variable step size (WVSS) and (b) the gradient spectral variance smoothing (GSVS). In AEC simulations, the WVSS-GSVS-FDAF-PEM-AFROW algorithm obtains outstanding robustness and smooth adaptation in highly adverse scenarios such as in bursting DT at high levels, and in a change of acoustic path during continuous DT. Similarly, in AFC simulations, the algorithm outperforms state-of-the-art algorithms when using a low-order near-end speech model and in colored non-stationary noise.

Inside a Chinese Communist Municipal Newspaper: Purges at the Beijing Daily

The Beijing Daily, the flagship media outlet of the Beijing Municipal Party, was one of the most influential newspapers established in the early years of the People’s Republic of China. The newspaper’s principal purpose was to propagate the remarkable achievements of the Chinese Communist Party and to demonstrate the superiority of the Chinese socialist system over the capitalist one. Newly available archival sources reveal a depressing and disturbing story behind the façade of authoritative reporting: an interlocking system of control of editorial management, stringent censorship, skillful manipulation of news, and carefully selected readers’ letters in praise of the Communist regime. In the early 1960s, in contrast to the harmonious picture of Chinese society depicted by the newspaper, senior editorial staff were caught in the middle of life-and-death ideological infighting between the radical Maoists and the pragmatists in the central Party leadership. The staff used a variety of techniques – double talk, fence-sitting, paying lip service to the official lines and conducting self-criticism – to navigate through the perilous political shoals. But they were eventually purged by the Maoists during the Cultural Revolution for siding with the pragmatists. Chinese journalists, including the Beijing Daily staff who worked in the system, lived a precarious life in the authoritarian environment.

Ennahda Islamists and the Test of Government in Tunisia

After winning the 2011 elections, the Ennahda Islamist Party was the majority partner in successive coalition governments, whose poor performance – namely in the economic and security fields – disappointed the people’s high post-revolutionary expectations. Opponents accused Ennahda of incompetence, greed for power and double talk. Many of the Ennahda-led governments’ failures were due to factors beyond their control, but some did indeed depend on Ennahda’s own political weaknesses. Nevertheless, Ennahda contributed positively to the overall development of Tunisia’s political transition thanks to its moderation and pragmatism and its contribution remains paramount for the democratic consolidation of Tunisia and other political Islamic actors.

반향제거기의 수렴전 동시통화검출

In this paper, we proposed a performance improvement method of the double talk detector which can operate before the echo canceller converges. Microphone input signal is filtered by the linear prediction filter and this filtered signal is used for detection. The coefficients of the linear prediction filter are given by the far-end talker signal. During single talk, filtered signal has low power since the characteristics of the echo signal is similar with those of the far-end talker signal. But, during double talk, the filtered signal does not have low power because the signal of different characteristics is included in the microphone signal. Double talk is detected by this difference. Simulations using real speech signals verified that the proposed method outperformed the conventional methods.

A Novel Double Talk Echo Canceller Algorithm Using Multi Delay Filter

Echo is a major problem in voice communication system. Several methods have been proposed to overcome this problem. Recently, a fast converging algorithm called Block Robust Proportionate Normalized Least Mean Squares (BRPNLMS++) against double-talk has been proposed. This paper presents a novel algorithm called (MDF-BRPNLMS++) based on the BRPNLMS++and the Multi-Delay Filter (MDF) algorithms. The proposed method allows reducing considerably the execution time, due to the use of the MDF, and reaching faster convergence by estimating the update step-size at each block iteration. In addition, the proposed method does not require a Double- Talk Detector (DTD) which contributes in reducing the required computational power. Simulation results have been performed using Matlab and prove a good agreement with the theoretical results.

A Single-Channel MVDR Filter for Acoustic Echo Suppression

Acoustic echo suppression techniques for full-duplex communication in low-complexity systems are commonly known to introduce distortion to the desired signal (i.e., near-end speech). Moreover, most traditional echo control techniques typically require accurately detecting the contribution of the near-end speaker to the microphone signal (“double talk”). In this letter, we propose a novel approach to acoustic echo suppression, which aims at extracting the near-end signal using a constraint for minimizing the distortion, and without requiring a double-talk detector.

음성인식 로봇을 위한 동시통화검출 기반의 강인한 음성 끝점 검출

본 논문에서는 반향이 큰 로봇 환경에 강인한 음성 끝점 검출 방법을 제안한다. 양방향 대화 로봇과 같이 반향대 신호 비가 -5 dB 이하인 반향환경에서는, 반향제거기의 성능이 저하되어 사용자 음성 에너지와 비슷한 크기의 에너지를 갖는 잔여반향이 생긴다. 잡음에 강인한 기존의 음성 끝점검출 방법이라도, 사용자 음성과 비슷한 수준의 에너지를 갖는 잔여반향은 음성으로 오검출하기 때문에 정확한 음성 끝점검출이 어렵다. 반향 환경에 강인한 끝점검출을 위해, 본 논문에서는 음성/반향 구간 판별에 좋은 성능을 보이는 동시통화검출의 결과를 기존의 음성끝점검출 방법과 AND 연산하여 음성끝점검출기를 구성하였다. 제안하는 방법의 평가를 위해 반향이 큰 환경에서 고립단어 인식을 실험하였고, 다양한 실험환경에서 기존 음성 끝점검출 방법보다 평균 30 % 이상의 인식 성능 향상을 확인할 수 있었다. This paper presents a robust speech end-point detector using double talk detection in echoic conditioned speech recognition robot. The proposed method consists of combining conventional end-point detector result and double talk detector result. We have tested the proposed method in isolated word recognition system under echoic conditioned environment. As a result, the proposed algorithm shows superior performance of 30 % to the available techniques in the points of speech recognition rates.

Enhancement of Residual Echo for Robust Acoustic Echo Cancellation

This paper examines the technique of using a noise-suppressing nonlinearity in the adaptive filter error feedback-loop of an acoustic echo canceler (AEC) based on the least mean square (LMS) algorithm when there is an interference at the near end. The source of distortion may be linear, such as local speech or background noise, or nonlinear due to speech coding used in the telecommunication networks. Detailed derivation of the error recovery nonlinearity (ERN), which “enhances” the filter estimation error prior to the adaptation in order to assist the linear adaptation process, will be provided. Connections to other existing AEC and signal enhancement techniques will be revealed. In particular, the error enhancement technique is well-founded in the information-theoretic sense and has strong ties to independent component analysis (ICA), which is the basis for blind source separation (BSS) that permits unsupervised adaptation in the presence of multiple interfering signals. The single-channel AEC problem can be viewed as a special case of semi-blind source separation (SBSS) where one of the source signals is partially known, i.e., the far-end microphone signal that generates the near-end acoustic echo. The system approach to robust AEC will be motivated, where a proper integration of the LMS algorithm with the ERN into the AEC “system” allows for continuous and stable adaptation even during double talk without precise estimation of the signal statistics. The error enhancement paradigm encompasses many traditional signal enhancement techniques and opens up an entirely new avenue for solving the AEC problem in a real-world setting.

METHOD OF DETECTING A DOUBLE TALK SITUATION FOR A “HANDS-FREE” TELEPHONE DEVICE

The device comprises a microphone for detecting a speech signal from a near speaker, and a loudspeaker for reproducing a speech signal from a remote speaker. The processing for canceling the interfering acoustic echo implements an adaptive linear filtering algorithm. Double talk situations are detected by: evaluating an index representative of the convergence or divergence of the algorithm; assessing a predetermined condition for detecting a double talk situation; and if the condition is satisfied, modifying at least one parameter of the algorithm in response to the detection. The representative index may be the norm of the gradient vector describing the adaptation of the filter from one iteration of the algorithm to the next, the conditions being a comparison between the gradient and a threshold. The parameter that is modified double talk situation may be the adaptation stepsize of the algorithm, and also the gain control of an echo suppression stage.

A New Echo Cancellation Algorithm without Double-Talk Detection Based on Correlation Function

In an adaptive echo canceller, the detection algorithm able to distinguish echo path change (EPC) from double-talk (DT) is vital to ensure that adaptive filter tap coefficients are updated in case of EPC and frozen during the DT period. The paper presents a new echo cancel algorithm, which can protect the adaptive filter performance during double-talk in acoustic echo cancellation of teleconference without setting a detector. A judgment value can be directly used in the iteration formula to control the iteration speed of the filter, which composed of the correlation of the far-end signal and near-end received signal, the pre-correlation of the error signal. The computer simulation results verify that the mentioned algorithm has the good double talk protection performance, and it is very useful and efficient in distinguishing EPC from DT but with less computational complexity contrast to the congener algorithm.

Design and Implementation on a Sub-band based Acoustic Echo Cancellation Approach

This paper describes the design and implementation of a sub-band based acoustic echo cancellation approach, which incorporates the normalized least mean square algorithm and the double talk detection algorithm. According to the simulation, the proposed approach works well in the modest linear noisy environment. Since the proposed approach is implemented in fix-pointed C, it can be easily ported into fixed-point DSPs to cancel acoustic echo in real systems.

Review: Essence of Indecision Diefenbaker's Nuclear Policy

ESSENCE OF INDECISION Diefenbaker's Nuclear Policy, 1957-1963 Patricia I. McMahon Montreal: McGill-Queen's University Press, 2009. 246PP, $85.00 cloth ISBN 978-0-7735-3498-8Five decades after it took place, Canada's nuclear weapons debate of the late1950S and early 60s remains poorly understood. This is a consequence of several factors - the long-standing tendency of Canadian defence scholars and historians to turn their attention elsewhere, the fact that most Canadians have only a limited knowledge of their own history, and perhaps even the discouragement of this country's foreign policy elites (who might prefer that Canadians not know about this entire affair) - but the net result is that the debate and final decision remains a subject of study.Patricia I. McMahon's book, Essence of Indecision, is the most recent attempt to try to make sense of this episode. Building on a relatively smaU body of scholarship (perhaps the best known of which remains Jon McLin's seminal 1967 work Canada's Changing Defence Policy), McMahon chaUenges the consensus view by arguing that Prime Minister John was not indecisive in being unable to determine whether Canada should accept US nuclear weapons during his period in office. Rather, his inability to reach a final decision was the result of considerations. In particular, Diefenbaker's Conservatives were attempting to navigate government waters for the first time in decades, and the prime minister was acutely aware of the political consequences of making the wrong decision. At the same time, the government had come under withering criticism for its decisions on other defence issues (especially establishing NORAD in 1957-58 and cancelling the Avro Arrow in 1959), thereby making the nuclear weapons decision even more difficult.Without question, McMahon's task is not easy. As I and others have written, dithered for virtuaUy his entire tenure as prime minister. Even as his time in office was coming to an end in early 1963, he was still unable to articulate a clear position. His speech in January of that year - intended to clarify his thinking in the aftermath of the Cuban missile crisis - remains a masterpiece of double talk and obfuscation. During his six years in office, steadily moved from one side of the debate to the other. He spent his first four years laying the groundwork to accept nuclear weapons, but over the last two years of his term he did everything possible to ensure that Canada did not accept the weapons that he had previously said it would.The consensus view is that this change was the result of several factors, three of which stood out. First, appointed Howard Green - a man committed to disarmament - as secretary of state for external affairs in mid1959. Second, contrary to the opinion polls of the day, believed that the majority of Canadians opposed nuclear weapons, a condusion he reached largely by reading his personal mail. Finally, in this period arms control talks between the US and the USSR got underway, the goal of which was general and complete disarmament and an end to nudear testing.McMahon argues that these explanations are insufficient, and that to understand the delay one must first understand Diefenbaker's tenuous political position (even after winning an unprecedented majority in 1958). As the author notes in a critical passage, Diefenbaker feared the potential political fallout that could accompany the acquisition of nuclear weapons... [and this] is what lent an air of indecision to his behaviour (x). According to McMahon, Diefenbaker's delay was understandable, and his recognition of the political risks that nuclear acquisition entailed largely explains his difficulty in coming to a final decision.McMahon insists that always wanted Canada to acquire the weapons, but the timing was never right. …

Reflections of a Country Plastic Surgeon

One of the great things about being a country plastic surgeon in a small city in Ontario is that there are so many operations to perform; the problem is how to get enough operating time. One of the negative things is the system, which works on a budget regardless of the amount of work. So, to not overspend on the budget, patients have longer wait times or go to other hospitals where the budget is bigger. Anyway, my resolution is not to discuss religion, politics or Medicare – in Canada, that is the same thing. Despite my resolution, I have to say something when patients ask me, “Why can’t I have my basal cell treated now?”; I say, “I have the time, the hospital does not. They have to meet their budget”. Amazingly, most Canadians accept this; a far cry from the independent ‘outback’ personalities I grew up with as a child – “Nobody tells me what to plant!” On the other hand, maybe I have misjudged Canadians. There is a strong streak in people here that to actually pay for something when you could get it free would be the height of foolishness, and these people are canny! Free trumps right away any time. There is the occasional mild complaining, but nobody ever does anything about it. Country people are tough and stoic, and are proud of it. To work in the country, the plastic surgeon needs to be bilingual, and add ‘country talk’ to ‘city talk’. Patients here are down to earth and accepting, but you have to be able to sum it up quickly and to the point; no fancy double talk or complex informed consents. They already know what could go wrong. To tell them is insulting. You just say what they need and why. They already know anyway because their general practitioner told them. Many even come to the first visit thinking you are going to operate on the spot without having seen them first because their general practitioner has decided what operation they need. If you have a ear for it, it is possible to speak the local dialect if you keep your ears open and enjoy. Things I have heard are the following: irony-deficient anemia, quite a wee while, umbrella 30, mammeogram, gangrion and gangilon, chicken pops, chyriopractor and chiorpractor. Some others are the following, “Hello, what do you know? Nothing, what do you know?” Forget the difference between few and less; good and well. Those are gone forever, even on CBC. Now it’s right to first names and, ‘I put some Dettol on’er, Doc and she healed up real good”. When I see people in ambulatory care, many people prefer to call it ambletory care, and so do I. Talking to teens who bash their hands on concrete walls in a testosterone fit is easy. Just do it like a TV hockey interview. And drop your ‘g’s’. It’s ‘goin’ not ‘going’. How about the following: “The doc put a splinter on it and I just got X-rated”. My theory is that people know how to speak properly, but talking country is just a lot funnier and that’s why they do it. Having a country plastic surgery practice means patients are stoic and accepting. You can perform many surgeries under local anesthesia; patients love the idea of not being ‘put out’ and having a ‘double double’ before surgery. For non-Canadians, that means a gigantic coffee with lots of sugar – enough to cause diabetes. Although, there is one problem, and that is getting more operating time without being labelled a ‘whistle blower’. Country people will wait and never criticize the system they have come to love; the question is how long a wait is too long? Figure 1

New Improved echo canceller based on Normalized LMS Adaptive filter for Single talk and Double talk Detection, Subband echo cancellation, Acoustic Echo cancellation

A modified version of normalized least mean square (NLMS) algorithm that achieves faster convergence in time domain with a marginal increment in implementation complexity than the existing one is proposed. Variations on the Normalized LMS (NLMS) algorithm have been made to improve convergence rate, Signal to Noise Ratio (SNR) and Steady state characteristics for Single talk and Double talk detection, Sub band Echo cancellation and Acoustic echo cancellation. The echo canceller is intended to cancel wireline echo from the PSTN due to the 2-to-4 wire hybrid conversion impedance mismatch. The echo canceller will also cope with acoustic echo originating from the wireline phone as well as analog cellular hands-free calls in the near-end path. Traditionally, speech enhancement techniques in VOIP or mobile networks are done in the transcoding unit operating on the uncoded signal. This means that the signal coming from the mobile terminals for example has to be decoded, enhanced and encoded again; these operations obviously introduce delays other than being computationally intensive and particularly prone to adding further quantization noise. Hence the need to design a echo canceller that offers a better convergence rate and Steady state characteristics.