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11
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The phonetic component
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11.1 Overview
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The phonetic component, PHONET, accepts input from the fundamental frequency
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component FOTARG (in the form of an array of phonetic segment names, and a
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segmental stress feature, segmental duration, and two fundamental frequency tar-
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gets for each phone), and produces output values for 20 synthesizer control
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parameters every 5 msec. This chapter concemns the strategy for phonetic-to-
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parametric rule development and a summary of the form and content of individual
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rules for control parameter specification.
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11.1.1 “Stored prosodics” synthesis
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The phonetic component PHONET and synthesizer components can be operated in
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stand-alone mode in which the phonetic segment string, durations, and fundamen-
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tal frequency contour specification that form the input to PHONET are hand-tuned
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to be as accurate as possible. For example, one might record a natural version of a
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sentence, extract fundamental frequency, measure segmental durations, select
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phonetic segments according to the pronunciation used by the real speaker, and
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format this information in a way that is compatible with PHONET input. The ad-
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vantage of this approach is the naturalness of the speech that can be produced with
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an input representation consisting of about 250 bits per second of speech.
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This method of generating speech might be compared with the Texas
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Instruments’ Speak-’N-Spell vocoder synthesizer. We suspect that the overall in-
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telligibility and naturalness of the MITalk “stored-prosodics™ synthesis is slightly
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better at 250 bits/second than Speak-’N-Spell at 1200 bits/second. However, the
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significant disadvantage of MITalk is that there is no automatic procedure for
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determination of input parameter data for PHONET, whereas Speak-’N-Spell syn-
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thesis can be prepared automatically from a linear-prediction vocoder analyzer
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with only minimal selection and hand tuning.
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11.1.2 Structure of PHONET
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The phonetic component includes a large array of target values for various control
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parameters for each of about 60 phonetic segment types. Smoothing between tar-
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get values depends on time constants computed by rule, as well as depending on
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108
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