Double-talk Detector Research Articles

A multichannel acoustic echo canceler double‐talk detector based on a normalized cross‐correlation matrix

AbstractMultichannel acoustic echo cancellation is basically composed of two parts. One part is a multichannel system identification problem which is nontrivial to solve. The other part, which is also nontrivial, is the so‐called double‐talk detection problem. Near‐end speech detection is based on a test statistic. Recently, a new double‐talk test statistic based on the normalized cross‐correlation vector was proposed For the single‐channel case. Obviously, in the multichannel case, there are several solutions, but what should be the optimal one is not yet known. Then, a fundamental question arises: how do we deal optimally with multiple channels? In this paper, we generalize the idea of normalized cross‐correlation vector (single‐channel) to the matrix case (multichannel), derive a frequency‐domain version, and show how to combine both the multichannel frequency‐domain adaptive filter and the multichannel double‐talk detector.

Integrated echo and noise canceler for hands-free applications

An integrated acoustic echo and noise canceler is proposed for hands-free telephony applications. The proposed system includes a computationally efficient double-talk detection (DTD) method and a residual echo cancellation algorithm. The DTD method uses two cross-correlation coefficients and is robust in adverse conditions. In the residual echo cancellation approach, a linear prediction error filter removes the short-term correlation of the residual echo and the resulting whitened residual echo is canceled by a noise-reduction filter. The proposed system was implemented using a general purpose digital signal processor (DSP) with 16-b arithmetic.

A frequency-domain double-talk detector based on a normalized cross-correlation vector

A key component for hands-free, full-duplex, communication technology is the echo canceler. An echo canceler consists primarily of an adaptive filter and a control device called the double-talk detector. We derive a test statistic based on a normalized cross-correlation vector for the multichannel frequency-domain adaptive algorithm. The advantages of this approach are: low computational complexity, simplicity of implementation, and better performance than the classical Geigel algorithm.

A robust fuzzy logic-based step-gain control for adaptive filters in acoustic echo cancellation

Step-gain control is crucial for acoustic echo cancelers. Most double-talk detectors and step-gain estimators become unreliable in certain situations. In this contribution, we combine a step-gain estimation method with a double-talk detector by fuzzy logic. This control is robust and efficient while requiring only very little additional complexity.

Acoustic echo cancellation using iterative-maximal-length correlation and double-talk detection

The conventional maximal-length-correlation (MLC) algorithm to estimate room impulse response for adaptive echo cancellation (AEC) is disturbed by both far-end and near-end speech. In this paper, a new iterative-maximal-length-correlation (IMLC) algorithm is proposed to reduce the far-end speech interference. To avoid the near-end interference, a new double-talk detection (DTD) method is proposed by tracking the squared coefficients errors of the AEC filter. This DTD method has well-separated detection margins among single-talk (ST), double-talk (DT), and echo path changes. Statistical analysis and computer simulations confirm that our proposed IMLC-DTD algorithm outperforms conventional methods.

A double-talk detector for acoustic echo cancellation applications

In acoustic echo cancellation applications, the presence of near-end speech causes divergence of the adaptive filter which is used to model the echo path. A robust acoustic echo canceler is the one which is equipped with an algorithm that detects periods of double talk and puts the adaptive algorithm into a double-talk handling mode. This paper proposes a double-talk detector based on an angle measure between two vectors comprising samples of input signal to the near-end microphone and the estimated echo at the output of the adaptive filter. Whenever the double talk is detected, the adaptive algorithm is frozen. The proposed detector has a quick reaction to the onset and cessation of the double talk and we illustrate this with a few simulations with pre-recorded speech segments. Performance of the subband adaptive filter (Navaneetha Krishnan et al., Proceedings of the Eighth IEEE DSP Workshop, Utah, August, 1998) with the proposed double-talk detector is compared with that of Doherty and Porayath (IEEE Trans. Circuits Systems-II (May 1997) 389–396). We used ERLE and coefficient error vector norm as the performance measures.

A new class of doubletalk detectors based on cross-correlation

A doubletalk detector (DTD) is used with an echo canceler to sense when far-end speech is corrupted by near-end speech. Its role is to freeze the adaptation of the model filter when near-end speech is present in order to avoid divergence of the adaptive algorithm. Several authors have proposed to use the cross-correlation coefficient vector between the input signal vector x and the scalar output y for a DTD. We show in this paper that this measure is not appropriate and propose a modified form that meets, in an optimal way, the needs for an efficient DTD. By extension, we also propose a definition of the normalized cross-correlation matrix between two vectors and show a link with the coherence function.

Double-talk robust fast converging algorithms for network echo cancellation

There is a need for echo cancelers for echo paths with long impulse responses (/spl ges/64 ms). This in turn creates a need for more rapidly converging algorithms in order to meet the specifications for network echo cancelers. Faster convergence, however, in general implies a higher sensitivity to near-end disturbances, especially Previously, a fast converging algorithm has been proposed called proportionate normalized least mean squares (PNLMS) algorithm. This algorithm exploits the sparseness of the echo path and has the advantage that no detection of active coefficients is needed. In this paper we propose a method for making the PNLMS algorithm more robust against double-talk. The slower divergence rate of these algorithms in combination with a standard Geigel double-talk detector improves the performance of a network echo canceler considerably during double-talk. The principle is based on a scaled nonlinearity which is applied to the residual error signal. This results in the robust PNLMS algorithm which diverges much slower than PNLMS and standard NLMS. Tradeoff between convergence and divergence rate is easily adjusted with one parameter and the added complexity is about seven instructions per sample which is less than 0.3% of the total load of a PNLMS algorithm with 512 filter coefficients. A generalization of the robust PNLMS algorithm to a robust proportionate affine projection algorithm (APA) is also presented. It converges very fast, and unlike PNLMS, is not as dependent on the assumption of a sparse echo path response. The complexity of the robust proportionate APA of order two is roughly the same as that of PNLMS.

An objective technique for evaluating doubletalk detectors in acoustic echo cancelers

Echo cancelers commonly employ a doubletalk detector (DTD), which is essential to keep the adaptive filter from diverging in the presence of near-end speech and other disruptive noise. There have been numerous algorithms to detect doubletalk in an acoustic echo canceler (AEC). In those applications, typically, the threshold is chosen only by some heuristic method and the performance evaluation is very subjective. In this study, we develop a way to objectively evaluate DTD algorithms based on the standard statistical methods of detection theory. A receiver operating characteristic (ROC) is derived to characterize DTD performance. Several DTD algorithms are examined and simulated under typical real-world operating conditions using measured room responses and signals taken from a digital speech database. The DTD methods are then evaluated and compared using the ROC metric.

A double-talk resistant subband echo canceller

A recursive transfer function estimation algorithm is presented and analyzed. Applications can be found in either line or acoustic echo cancellation. The proposed algorithm is robust against burst disturbances that are caused by detection misses of double-talk present at the output of the echo path. A frequency-domain technique is used and a robust score function is derived from a criterion that is valid in the application. Analysis of the robust algorithm shows that good performance is to be expected. The performance of the algorithm when operated on real-life speech data in a full duplex communication system is shown by examples. Double-talk detection misses are shown to be well handled by the robust algorithm; yet, convergence rate and variance efficiency are as high as that of a non-robust least-squares algorithm.

Control of a hands-free telephone set

In this paper, we discuss different methods of double talk detection used for echo cancellation in a hands-free telephone set. We deduce a general state-space representation of the set, which leads to state-dependent structures for stepsize control. The approach is further generalized by introducing fuzzy logic and fuzzy state memberships. Finally, first results are shown which are obtained with identical detection methods, but applying different control structures.

A double-talk detector based on coherence

We address the problem of detecting double-talk in a full duplex transmission line. A new double-talk detector (DTD) based on measuring the similarity between the far- and near-end speech signals is proposed. The detector is block oriented and operates in the frequency domain where the similarity between the signals is measured by means of the coherence function. The coherence is estimated with a short sequence of data by exploiting the multiple window spectrum estimation technique. Theoretical evaluation and examples of its performance are presented. The proposed DTD operates accurately in a wide range of situations, i.e., a difference in speech levels and hybrid attenuations ranging from 0 to 20 dB.

A multirate acoustic echo canceler structure

A new subband echo canceler (SBEC) structure is proposed to reduce the transmission delay introduced by conventional SBEC structures, without distorting the near-end signal. The proposed structure is based on computing two output errors, one for using during single-talk and the other one for using during double-talk periods. With the SBEC structure we propose a double-talk detector with a subband configuration which allows a fast and accurate detection of double-talk periods, enabling the SBEC algorithm to track changes in the echo path impulse response when the near-end signal is absent. Computer simulations using actual speech signals, and subjective evaluation tests are given to show the convergence performance, tracking and double-talk detection ability, of the proposed scheme.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency-domain adaptive filtering with applications to acoustic echo cancellation

In this paper an algorithm is presented for adaptive filtering in the frequency-domain with application to acoustic echo cancellation. This algorithm, called generalized multi-delay filter(GMDFα, is derived from the frequency-domain implementation of the time-domain block least mean square algorithm. Two different implementations are introduced, one based on the discrete Fourier transform(dft) and one based on the discrete Hartley transform(DHT); some results on fixed-point implementation of the algorithm are provided which are compared to results obtained from floating point implementation. Finally, the application of thegmdfα algorithm to acoustic echo cancellation, in hand-free telephone systems, is detailed. Some control strategies are presented; in particular a novel double-talk detector based on a spectral dissimilarity measure is introduced ; also, a twin-filter structure which significantly enhances the echo rejection is derived.

Development and analysis of distributed acoustic echo cancellation microphone system

Abstract Acoustic echo cancellation using an adaptive transversal filter and the least mean square algorithm is the most effective technique of reducing acoustic echoes in a hands-free telephone system. However, a very high-order adaptive filter and multiple echo paths for each microphone result in difficulties in algorithm convergence and hardware implementation. This paper presents a distributed system which performs acoustic echo cancellation in the microphone unit. Each acoustic echo cancellation microphone unit has two closely spaced directional microphones pointing in opposite directions and a much lower order adaptive filter than in the earlier systems. Computer simulations were conducted based on real speech data collected from a typical conference room. Finally, a robust double-talk detector, which identifies three modes of operation, was developed and tested in real-time

Distributed acoustic echo cancellation system with double-talk detector

The acoustic echo cancellation system using the least-mean-square algorithm is an effective technique to reduce acoustic echoes in a hands-free telephone system. However, very high-order adaptive filters and multiple echo paths have computational and convergence problems. Recently, a new acoustic echo cancellation microphone (AECM) system [S. M. Kuo and Z. Pan, J. Acoust. Soc. Am. 93, 1629–1636 (1993)], which uses two closely spaced directional microphones and a low-order adaptive filter, was proposed to solve these problems. In order to make the AECM system work automatically, a double-talk detector, which is presented in this paper, is required. This detector utilizes the power difference between the system output signal and the microphone output signal. Computer simulations were conducted to demonstrate the effectiveness of the detectors. The complete AECM system was implemented on the TMS320C25, and real-time experiments were conducted in the conference room.

A new double-talk detection algorithm based on the orthogonality theorem

The algorithm not only prevents the echo canceler from being disturbed by double talking but also tracks the echo path variations. Although the algorithm requires more computation and storage than conventional algorithms, excellent double-talk interference protection performance and echo path tracking have been obtained. >

An acoustic echo canceler implemented with AT&amp;T DSP16A

Acoustic echo control in teleconferencing and hand-free phone systems is not trivial because of its special characteristics. Many acoustic cancellation algorithms have been published in recent years but they are either of theoretical consideration or are computer simulations with complicated computation burdens, which makes real-time implementation impossible. In this paper, a two-band scheme is proposed to realize an acoustic echo canceler with an AT&amp;T WE DSP16A microprocessor. The structure of the algorithm is optimized so it can give an echo return loss enhancement (ERLE) of more than 25 dB. A double talk detector is developed with the subband adaptive algorithm so that it will ensure full duplex communication. Performance of this canceler is evaluated with both computer simulation results and real-time test results.