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14
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Implementation
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14.1 Conceptual organization
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Throughout this book, emphasis has been placed on the representation of various
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data forms and rules, together with transformations between these representations.
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A strong effort has been made to exclude all reference to implementation concerns
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from these discussions. At this point, however, it is appropriate to address these
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issues, thus giving a view of the conceptual framework in which this research was
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done, as well as a perspective on economically viable implementations that can’
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deliver the overall text-to-speech capability in real-time. With these goals in mind,
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we discuss first the overall conceptual organization of the MITalk system, fol-
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lowed by a description of the development system used as a research vehicle over
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the course of a dozen years, the requirements for a “performance system” suitable
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for practical applications, and finally, a discussion of the current system, together
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with examples, which serves as the basis for distribution of the MITalk system
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from MIT.
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The overall conceptual organization of the MITalk system can be viewed on
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two levels. At the highest level, the system is viewed as an analysis/synthesis sys-
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tem. Itis based on the premise that in order to transform an input textual represen-
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tation (as a string of ASCII characters) to an output synthesized speech waveform,
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it is necessary to first analyze the text into an underlying abstract linguistic
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representation which can then be used as the initial basis for synthesizing the
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waveform. In this sense, the text and speech waveform representations are seen as
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two different surface representations of a common, underlying linguistic represen-
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tation which unites these two surface forms. Thus, the first part of the system is
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oriented to transforming the input textual representation into a narrow phonetic
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transcription which includes the names of the constituent phonemes, stress marks,
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and syntactic boundaries at the syllable, morph, word, phrase, and sentence levels.
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It is an implicit assumption of the system that this transcription is sufficient to
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serve as the input for the synthesis routines which generate the timing framework,
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the pitch contour, and the detailed control parameters (updated at 5 msec intervals)
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which specify the nature of the vocal tract model, which in turn produces the final
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output synthetic speech waveform.
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172
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