Puneet Gupta and Anil Kumar

While IP telephony is gaining popularity and is the direction towards the future, it comes with its own set of challenges. While there are multiple aspects like jitter and packet loss management that come into picture for combating the 'IP' (or network) part of the ecosystem, there is a whole cluster of pre/post processing challenges that one needs to face to provide an overall quality solution.

One of the major challenges in IP telephony pre-processing lies in cancelling acoustic echo that marks the speakerphone operation. Although speaker-to-microphone coupling occurs in traditional PSTN telephony too, the echo is less annoying due to really low end-to-end latencies (<30 milliseconds round trip delay). In IP networks, however, the delay tends to be much higher (>100milliseconds in a typical case), which makes acoustic echo much more noticeable and hence aggravates the problem due to echo. Despite of the fact that the cancellation of acoustic echo forms a cornerstone of voice quality assessment by users, much is not understood about the dynamics involving an acoustic echo canceller (AEC).

In this paper, we provide an introduction to various aspects of AEC including its generation and characteristics, primary quality metrics, challenges involved in implementation, the impact of hardware on AEC performance in a phone and some information on testing an AEC.