Prosodic rules for the implementation of phrase boundaries in synthetic speech

From previous research it is known that speakers use the prosodic cues pause and pitch to audibly structure their spoken messages. Listeners, on the other hand, use these phonetic cues to determine the degree of disjuncture in the flow of speech, which supposedly helps them to process the meaning of the utterances. In the research reported here, a professional speaker's phrasing behavior was modeled in various sets of rules, corresponding to different levels of prosodic boundary strength. These phrasing rules were evaluated as to their acceptability and it appeared that several of them improve the quality of the synthetic speech. The rule set implementing five levels of boundary strength improved this quality more than rule sets with fewer levels. In fact, it appeared that this rule set produces synthetic speech which is prosodically almost as good as a copy-synthesis version with natural prosody.