Implementation Of Echo Canceller Research Articles

Statistical Analysis of Doubletalk Detection for Calibration and Performance Evaluation

Doubletalk detection is an important part of a practical echo canceller implementation, but a difficult problem is calibrating the doubletalk detector for arbitrary environments and input signals. In this paper, it is shown that a statistical model of a doubletalk detection variable's probability density function (PDF) can be used to obtain an optimal detection threshold and expected detection performance curves. In particular, a statistical analysis of a recently proposed cross-correlation-based doubletalk detector is presented. The doubletalk detection variable is modeled in terms of its constituent parameter estimators, resulting in conditional PDFs in the absence and presence of doubletalk. These are used to obtain a signal-adaptive detection threshold for calibration, and to provide expected doubletalk detection probability. Simulations are presented comparing the theoretical and measured detection probability compared to a fixed detection threshold for speech input and doubletalk signals. The results indicate a close agreement with the proposed model for moderate-to-high levels of doubletalk

TMS32020 implementation of an adaptive recursive echo canceller

Recently, the application of adaptive recursive digital filters (ARDF) in echo cancellation has received considerable attention. This is because the ARDF can match a long echo path with fewer coefficients than the adaptive transversal digital filter (ATDF). Consequently, the ARDF has a shorter convergence time and smaller adaptation noise than the ATDF. Unfortunately the ARDF may exhibit instability during the adaption process. This paper outlines the development of an adaptive recursive echo canceller which is unconditionally stable. The new filter algorithm has been extensively tested in off-line simulations and this paper describes the on-line implementation of the echo canceller using a TMS32020 system. The signal processor is hosted by an IBM PC and is interfaced to a model data transmission network incorporating actual hybrid transformers. A realistic echo is thus available to evaluate the filter performance.