The Effects of Time Delay and Echoes on Telephone Conversations

Abstract

A brief history of the problem of echoes and delay in telephone connections is first given. Actual delays involved in typical circuits are shown. This is followed by a discussion of the effects of delay only on typical conversations. The sources of echo in typical telephone connections are then discussed, together with measures which have been taken to reduce echo by improving return loss. Methods of controlling the effects of delayed echo are then summarized; the summary includes a brief introduction to echo suppressors and some of the new problems they introduce.

ECOOSE: an echo cancellation object oriented simulation environment

“…Echo management first became necessary in the 1930's when international telephony introduced one way delays of up to 80 milliseconds(e.g. London-Hawaii [3]). Transmission over distances of this length requires amplification, which is only practical in systems which use 4 wires: 2 in each direction.…”

Non-linear echo cancellation - a Bayesian approach

“…London-Hawaii [3]). Transmission over distances of this length requires amplification, which is only practical in systems which use 4 wires: 2 in each direction.…”

“…The introduction of satellite links caused long delays of up to half a second [3]. The imperfections of echo suppression then became exacerbated.…”

Digital voice communication over digital radio links

“…It is well recognized that voice data is perishable and must be delivered within no more than 250 milliseconds (satellite delay), to avoid adverse psychoacoustic effect on the listener, [20], [8], [25];in this respect coa~puter data is more robust --intermediate buffering can be employed as long as necessary to achieve appropriate flow control.We will impose this delivery constraint on the PVPR and examine the ensuing implications.…”