Subjective evaluation of unsuppressed echo in simulated long-delay telephone communications

Abstract

The paper describes an experiment to measure the subjective effect of unsuppressed echo to determine the improvement in echo return loss required of echo cancellers in long-delay telephone communications. Using a simulated long-delay telephone connection of 16-5dB nominal overall reference equivalent, tests were carried out over a range of conditions in which the 1-way delay varied between 50 ms and 600 ms, and the echo return loss between 15dB and 50dB. Echo-path frequency characteristics which an echo canceller might cause in practice were represented by a flat characteristic and a characteristic decreasing in loss with increasing frequency. Because of the large number of test conditions (40) in the experiment, the experimental design is unique and is described.

Application Potential of Four Nontraditional Similarity Metrics in Hydrometeorology

“…), as perceived by a large number of people who respond to a test or survey (Williams and Moye 1971;Miyahara et al 1998;Wang et al 2004). Let N be the total number of responses obtained from the test or survey, in which people are asked to assign the object quality to one of K categories based on their perceived judgments.…”