A multiline computer voice response system utilizing ADPCM coded speech

In this paper we discuss the issues involved in implementing an automatic computer voice response system which is capable of serving up to ten independent output channels in real time. The system has been implemented on a Data General NOVA- 800 minicomputer. Individual isolated words and phrases are coded at a rate of 24 000 bits/s using a hardware adaptive, differential pulse-code modulation (ADPCM) coder, and stored on a fixed-head disk as a random access vocabulary. By exploiting the features of ADPCM coding, it is possible to create and edit automatically a vocabulary for the system from an analog tape recording of the spoken entries, with minimal operator intervention. To provide ten simultaneous output lines of speech which are independent of each other required the use of an efficient scheduling algorithm. Such an algorithm was provided by the computer manufacturer in their real-time multitasking system which was part of their Fortran software. Thus almost all the programming required to implement this real-time system was in Fortran, thereby providing flexibility and ease in making changes in the system. Initial applications of the voice response system are in computer aided voice wiring, automatic directory assistance, and experiments on speaker verification, but the system is sufficiently modular to adapt readily to other applications.