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Survey of speech synthesis technology
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The input to the rules includes phonemes, stress, word and morpheme boundaries,
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and syntactic structure.
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In time, these methods ought to be able to produce highly intelligible natural
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speech, but present results are frequently perceived to be somewhat unnatural and
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machine-like. This appears to be due mainly to the intricate complexity of the
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speech code and the fact that not all of the rules are known at this time. There is a
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particular need to improve on the specification of fundamental frequency and dura-
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tion algorithms, perhaps by making incremental improvements to current al-
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gorithms (Umeda, 1976; Klatt, 1979a; Maeda, 1974; O’Shaughnessy, 1977; Pierre-
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humbert, 1979).
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7.4 Applications
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7.4.1 Synthesis of arbitrary English sentences
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From the above discussion, it should be clear that there are a number of promising
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methods for synthesizing general English. To generate a particular utterance, one
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must know 1) the phonemic (or phonetic) representation for each word, 2) the
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stress pattern for each word, 3) aspects of the syntactic structure of the sentence,
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and 4) the locations of any words that are to receive semantic focus. This infor-
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mation would have to be stored in the computer for each utterance to be syn-
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thesized, or it might be generated from a deep-structure representation of the con-
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cept to be expressed (Woods et al., 1976; Young and Fallside, 1979).
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7.4.2 Synthesis of arbitrary English names
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Research at Bell Laboratories (Denes, 1979; Liberman, 1979; Olive, 1979) is
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directed at the ability to synthesize any name from a telephone directory for ap-
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plication in automated directory assistance. The linguistic problems associated
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with converting spelling to a phonetic representation and stress pattern are severe
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since it is sometimes necessary to guess the native language of the individual be-
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fore a good rendering of the pronunciation is possible (Liberman, 1979). Once a
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phonetic representation has been derived, this experimental system uses diphone
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synthesis (Olive, 1979) to generate a waveform. |
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7.4.3 Text-to-speech conversion
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The transformation of English text to speech is a much more formidable problem
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than the synthesis of an arbitrary sentence from a knowledge of its underlying lin-
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guistic representation. The text does not indicate everything that one would like to
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know (unless one builds a machine that can recognize the meaning of the text, and
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thereby disambiguate (frequently occurring) syntactic ambiguities, and determine
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semantic focus relations).
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79
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