ITU-T Recommendations

This Recommendation describes methods and procedures for conducting subjective performance evaluations of network echo cancellers.The deployment of digital technology in the Public Switched Telephone Network (PSTN) has had numerous advantages for users of the network as well as for network operators. These new technologies come at the price of increased transmission time, which increases the likelihood that any echo impairment will be annoying to voice users of the network. Hence, the deployment of echo cancellers in the network is widespread. Recommendations G.165 and G.168 define certain instrumental tests that must be met to ensure minimum performance of an echo canceller. However, there has been some concern that those tests do not address fully the echo cancellation needs of voice users of the network.Subjective testing is a commonly used method of assessing the performance of digital devices, including digital speech codecs and Digital Circuit Multiplication Equipment (DCME). This Recommendation defines natural extensions of those techniques to the subjective evaluation of echo cancellers.