Automatic user-adaptive speaking rate selection for information delivery

Today there are many services which provide information over the phone using a prerecorded or synthesized voice. These voices are invariant in speed. Humans giving information over the telephone, however, tend to adapt the speed of their presentation to suit the needs of the listener. This paper presents a preliminary model of this adaptation. In a corpus of simulated directory assistance dialogs the operator’s speed in number-giving correlates with the speed of the user’s initial response and with the user’s speaking rate. Multiple regression gives a formula which predicts appropriate speaking rates, and these predictions correlate (.46) with the speeds observed in good dialogs in the corpus. An experiment with 18 subjects suggests that users prefer a system which adapts its speed to the user in this way. 1. INFORMATION-GIVING BY VOICE Many commercial telephone dialogs include an information delivery phase, in which the system gives the user information such as a time, a price, a password, directions, a transaction or confirmation number, etc. As far as we know, all IVR and spoken dialog systems today provide information either by playing back a fixed, prerecorded voice, or by using a synthesized voice generated with fixed parameters. With information delivered at a single speed, invariant across users, it will be too fast for some users, such as nonnative speakers, children, and people in noisy environments, and too slow for others, such as business people in a hurry. In terms of time cost, if the speed is too slow there is a clear loss in user time, system time, and connection time; if the speed is too fast there is again a time loss, as the user has to wait for a repetition. Whereas the other phases of commercial dialogs (the greeting, call routing, caller identification, content understanding) have been well studied, and are indeed key concerns in the interactive voice response (IVR) business and ∗Ward is currently at the University of Texas at El Paso. Nakagawa is currently at IBM Japan. This work was supported in part by the International Communications Foundation, Tokyo, and by the Japanese Ministry of Education’s Prosody and Speech Processing Project, headed by Keikichi Hirose. in spoken dialog research, the information delivery phase has received less attention.