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Phonological rules

February 25, 2001
   
Phonological anlysis is one of the steps needed for a text-to-speech application. Cynthia takes the phonetic transcription of a piece of text and applies phonological rules for English to make adjustments to the pronunciation. The goal of a speech synthesizer is to arrive at a computerized model of the way humans speak. Here are some phonological rules that are implemented in Cynthia.
  • The lateral /l/ becomes velarized when it come at the end of a word either after a vowel or before a consonant.
    An example of this is the word sail [s ey l]. [l] is an alveolar approximant and is made by touching the front of the tongue to the alveolar ridge. In words like sail or walk, the tongue is moved towards the back of the mouth and the back of the tongue is raised to the velum.
  • A similar rule of English says that vowels are reduced when they come before an /l/ at the end of a syllable.
  • A nasal becomes a syllabic consonant if it comes at the end of a word and after an obstruent.
  • The pair [d y] can be converted to [jh] if it crosses a word boundary. There is a voiceless counterpart to this rule which converts [t y] to [ch] when the pair crosses a word boundary. Examples of these rules are the word pairs did you and eat yet. This rule is common in many Southern dialects of American English.
  • Vowels in unstressed syllables are normally reduced.
    A reduced vowel either becomes [ax] or [ih]. Since [ax] is used much more frequently than [ih], Cynthia reduces all unstressed vowels to [ax].