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The fundamental frequency generator
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10.4 The O’Shaughnessy fundamental frequency algorithm
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The algorithm may be considered as a cascade of two separate systems. The first,
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or High Level System, uses syntactic information to sketch the contour. The Low
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Level System uses information generated by the High Level System and additional
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phonemic data to detail the contour.
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10.4.1 High Level System
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The High Level System predicts a superposed FO contour by taking into considera-
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tion the sentence type, clause contour, phrase contour, and individual word con-
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tour. This contour is further augmented in the Low Level System by considering
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the effect of individual segments.
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10.4.2 Sentence type
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Two global-level tunes are assigned depending upon sentence type. Tune A is used
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primarily for declaratives. It causes a linear falling FO trend in the clause it is as-
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signed to, and a sharp fall on the last content word in the clause and on those
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words following it. The other tune, Tune B, is used for yes/no questions, that is,
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questions to which an answer of “yes” or “no” is expected. This tune causes a rise
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followed by a relatively flat FO trend and a sharp terminal rise.
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10.4.3 Clause contour
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The next factor affecting the contour is set by the syntactic boundaries. A sharp
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rise is stipulated at the beginning of a syntactic unit, and a sharp fall at the end. In
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practice, there is only one such contour for each sentence because clauses are not
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identified by the parser. This contour coincides with the tune contour.
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10.4.4 Phrase contour
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In phrases containing two or more content words, an initial FO rise is assigned
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beginning at the first content word and a final FO fall begins on the last content
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word. If the phrase is nonfinal, a continuation rise is placed on the last syllable of
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the last word.
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10.4.5 Word contour
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The individual content words within a phrase are given the most FO movement. In
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addition to the sharp rise and fall on the first and last content words in a phrase, a
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rise-fall contour is described on the stressed syllable of each content word. These
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excursions reflect the desire of a speaker to have listeners understand the less pre-
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dictable words in a sentence which are also those words which carry the most in-
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formation. Function words are very common and describe a syntactic structure
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which is easily recognized. Content words, on the other hand, must be emphasized
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somewhat for the utterance to be comprehended, since their occurrence is much
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103
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