Effects of Echo-Free Transmission Delay on Speech Patterns in Two-Way Telephone Conversations

Abstract

Satellite communication systems typically introduce round-trip transmission delays of at least 600 msec in telephone calls. Previous studies [e.g., E. T. Klemmer, Bell System Tech. J. 46, 1141–1147 (1967)] have sought subjective opinions of the acceptability of circuits containing long delays and no echo. In the present study, 16 pairs of male subjects conversed over an echo-free telephone circuit on zero delay and 600-msec round-trip delay, and 16 additional pairs conversed on 0- and 1200-msec delay. Each condition lasted 10 min. Subjects were selected to have minimal experience on delay circuits and were successfully led to believe they were conversing at all times over a standard circuit. This experiment examined differences in conversational behavior on the standard and delay circuits in the following aspects: (1) durations of “events” in ON-OFF patterns (talkspurts, mutual silences, etc.), (2) changes of pattern-generating model parameters [P. T. Brady, Bell System Tech. J. 48. 2445–2472 (1969)], (3) speaking levels, (4) instances of “confusion” observed by experimenter, and (5) reaction of subjects. Some model parameters change with delay, causing predictable changes in durations of certain events (double talks and mutual silences increase). Confusions are more numerous on delay. Speaking levels and subjects' opinions are unaffected by delay in their specialized task.