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Picturephone Service), but the first commercially viable instruments were actually produced and sold in 1992. In this case it took a bandwidth reduction (from 1.5 Mbps down to 19.2 Kbps) and a major cost reduction, as well as algorithm breakthroughs in voice and video coding and in modem design, to achieve this minor miracle.

Other technologies were able to leave the research laboratory rather rapidly, sometimes in response to national imperatives (e.g., miniaturization for the space program), and sometimes in response to business necessities. Hence, when fiber optic lines were first mass produced in the 1980s, it was estimated that it would take about two decades to convert the analog transmission facilities of the old Bell System to digital form. In reality the long-distance telephone network was fully digital by the end of 1989, fully 10 plus years before predicted. Similarly, in the case of cellular telephony, it was predicted that it would be about a decade before there would be 1 million cellular phones in use in the United States. By the end of 1992 (i.e., about 8 years after the beginning of the "cellular revolution"), the 10-millionth cellular phone was already operating in the United States, and the rate of growth of both cellular and wireless telephony was continuing unabated.

Now we come to the decade of the 1990s and we have already seen strong evidence that the key technologies that are evolving are those that support multimedia computing, multimedia communication, ease of use, portability, and flexibility. The vision of the 1990s is ubiquitous, low-cost, easy-to-use communication and computation for everyone. One of the key technologies that must evolve and grow to support this vision is that of voice processing. Although research in voice processing has been carried out for several decades, it has been the confluence of cheap computation (as embodied by modern digital signal processor chips), low-cost memory, and algorithm improvements that has stimulated a wide range of uses for voice processing technology across the spectrum of telecommunications and consumer, military, and specialized applications.

ELEMENTS OF VOICE PROCESSING TECHNOLOGY

The field of voice processing encompasses five broad technology areas, including:

• voice coding, the process of compressing the information in a voice signal so as to either transmit it or store it economically over a channel whose bandwidth is significantly smaller than that of the uncompressed signal;



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