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comprises the areas of knowledge required for human-machine communication by voice. This paper discusses commercial applications, which are beginning to have significant impacts on business and personal use. Commercial applications of speech interface technology, which first appeared in the early 1980s, are poised now in the early 1990s at a threshold of widespread practical application. Today's applications in speech interface technology utilize speech recognition or synthesis to simply translate spoken words into commands and text or vice versa with little regard to underlying meaning. In the future as applications for human-machine communication by voice grow, the need for natural-language-processing technology to permit speech interpretation will increase. The applications and developments described below represent some very important first steps into a future that will include systems capable of understanding natural conversational speech for transcription or spoken real-time translation. Today's applications are an important bridge to that future and represent the early and productive uses of speech interface technology.

Automatic speech recognition is the ability of machines to interpret speech in order to carry out commands or generate text. An important related area is automatic speaker recognition, which is the ability of machines to identify individuals based on the characteristics of their voices. Synthetic speech, or synonymously text-to-speech, is audible speech generated by machines from standard computer-stored text. These disciplines are closely related because they both involve an analysis and understanding of human speech production and perception mechanisms. In particular, the analysis of speech into its individual components (phones) and the characterization of the acoustic waveforms of these components are common to both disciplines. Speech recognition and speech synthesis are also closely coupled at the applications level—for example, for remote database access where visual displays are not available. The use of speech recognition for input and synthetic speech for output is a powerful combination that can transform any telephone into a fully intelligent node in a computer network.

BACKGROUND

Automatic speech recognition and text-to-speech technologies have been under development since the early days of modern electronic and computer technology in the middle part of this century. A phonemic-based text-to-speech system was demonstrated at the World's Fair in 1939 by AT&T Bell Laboratories; high-speed computers in the



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