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From text to speech: The MITalk system
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were given the label “function” are elevated to “content” importance in the FO al-
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gorithm. These are:
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¢ Demonstrative pronouns (this, those)
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¢ Contractions (we’ll, boys’ll)
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¢ Modals (should, might, will, can)
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¢ Quantifiers (several, many)
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¢ Interrogative adjectives (which, whose)
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The FO algorithm requires a specification of the number of syllables in each
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word, the location of the stressed syllable within the word, and information con-
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cerning syllable boundaries. This information is found in the PROSOD output file.
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The phonemic information in this file is also used to specify a structure for each
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syllable. This structure is an allowable ordering of voiced or unvoiced obstruents,
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sonorants, and a single vowel.
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10.3 Output
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There are two possible output files. One file is a stream of fundamental frequency
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values, one value for each 5 msec of the utterance. This file can be merged with
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the output of PHONET (discussed in Chapter 11) which gives values of the 20
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variable parameters each 5 msec. These values are calculated by determining the
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changes in FO during a syllable and using the duration of the segments within the
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syllable to describe a contour with constant slope (absolute value).
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A second method, the one currently in use, is to calculate rises and falls on
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each segment (an intermediate stage in the former method) and to use this infor-
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mation to specify FO target values for the midpoint of each segment and for the
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peak point at either the left or right boundary of stressed vowels in content words.
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Unspecified onset values for segments are determined by linear interpolation be-
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tween their midpoint target value and the midpoint target value of the preceding
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segment. This method allows FO values to be calculated every 5 msec using the
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same linear smoothing procedure which is used for some of the other parameters,
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modified slightly by the addition of the possible extra target value as input.
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Most peaks are assigned to the right boundary of the stressed vowel in a con-
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tent word. A fall (and possible continuation rise) following the rise which forms
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the peak is then assigned to the midpoint or right boundary of the following seg-
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ment, absorbing any fall or rise that might previously have been assigned to that
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segment. A peak is assigned to the left boundary of a “nuclear-stressed” syllable,
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i.e., the stressed syllable in the final content word of a phrase preceding a silence.
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Preceding unassigned rises or falls are absorbed in the assignment of the peak.
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102
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