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long-sought dictation machine, high-quality synthesis from text, and the ultimate in low bit-rate transmission of speech. It will also open the door to language-translating telephony, where the synthetic foreign translation can be in the voice of the originating talker.

INTRODUCTION

Speech is a preferred means for communication among humans. It is beginning to be a preferred means for communication between machines and humans. Increasingly, for well-delimited tasks, machines are able to emulate many of the capabilities of conversational exchange. The power of complex computers can therefore be harnessed to societal needs without burdening the user beyond knowledge of natural spoken language.

Because humans are designed to live in an air atmosphere, it was inevitable that they learn to convey information in the form of longitudinal waves supported by displacement of air molecules. But of the myriad types of acoustic information signals, speech is a very special kind. It is constrained in three important ways:

• by the physics of sound generation in the vocal system,
• by the properties of human hearing and perception, and
• by the conventions of language.

These constraints have been central to research in speech and remain of paramount importance today.

This paper proposes to comment on the field of speech communication in three veins:

• first, in drawing a brief perspective on the science;
• second, in suggesting critical directions of research; and
• third, in hazarding some technology projections.

FOUNDATIONS OF SPEECH TECHNOLOGY

Speech processing, as a science, might be considered to have been born from the evolution of electrical communication. Invention of the telephone, and the beginning of telecommunications as a business to serve society, stimulated work in network theory, transducer research, filter design, spectral analysis, psychoacoustics, modulation methods, and radio and cable transmission techniques. Early on, the acoustics and physiology of speech generation were identified as critical issues for understanding. They remain so today, even though much knowledge has been acquired. Alexander Graham Bell was among those



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