Telephone echo tests
D.L. Richards, G.A. Buck · Proceedings of the IEE Part B Electronic and Communication Engineering · 1960
Electrical reflection on telephone circuits having appreciable times of propagation can cause delayed sidetone effects subjectively similar to echo. The variations in subjects' tolerance of this echo is examined experimentally as a function of echo attenuation and delay. The dispersion of tolerance between subjects is also considered, and this yields information in a form suitable for planning telephone networks so that echo will not cause excessive inconvenience.