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The Affect of Convergence Speed in the Two-Path Method

The achievement of “telepresence” presents significant challenges to the acoustic signal processing field. In order for the users to feel they are physically present with the remote users requires the use of full-duplex hands-free communication devices. For acoustic echo cancellation (AEC), this makes modeling the echo path more difficult than in handset applications for a couple reasons. The first reason is the echo path of the acoustic environment is much longer than in a handset. The second reason is people and objects will be constantly moving within the acoustic environment, effectively modifying the echo path. To achieve the sense of presence, acoustic echo cancellation must allow the users to interrupt each other during conversation.

In the Two-Path Method for Acoustic Echo Cancellation, the application of two-path echo cancellation was introduced as an effective way to mitigate the challenges in hands-free acoustic environments. The rest of this article will further discuss the advantages of using the two-path method over traditional single-path echo cancelers.

In single-path echo cancellation an engineering tradeoff has to exist between the speed of convergence and the robustness to local disturbances of doubletalk. Also, the amount of divergence is governed by the level of the near-end speaker. The application of doubletalk detectors can only partially alleviate this problem as the probability of a doubletalk miss does not equal zero. In the two-path method an increased speed of convergence is beneficial to the performance of the system in handling doubletalk and echo path changes. The reason for this is simple. As mentioned previously, the faster the convergence of the system, the faster the divergence will be. Fast divergence is an advantage to the two-path method, because the foreground filter is only updated by the background filter when the perceived convergence of the system is better in the background. Hence, the two-path method will react faster to local disturbances as the convergence speed is increased.

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