The Contribution of Parsing to Prosodic Phrasing in an Experimental Text-to-Speech System

THE CONTRIBUTION OF PARSING TO PROSODIC PHRASING IN AN EXPERIMENTAL TEXT-TO-SPEECH SYSTEM ABSTRACT While various aspects of syntactic structure have been shown to bear on the determination of phrase- level prosody, the text-to-speech field has lacked a robust working system to test the possible relations between syntax and prosody. We describe an implemented system which uses the deterministic parser Fidditch to create the input for a set of prosody rules. The prosody rules generate a prosody tree that specifies the location and relative strength of prosodic phrase boundaries. These specifications are converted to annotations for the Bell Labs text-to-speech system that dictate modulations in pitch and duration for the input sentence. We discuss the results of an experiment to determine the performance of our system. We are encouraged by an initial 5 percent error rate and we see the design of the parser and the modularity of the system allowing changes that will upgrade this rate. INTRODUCTION We describe an experimental text-to-speech system that uses a deterministic parser and prosody rules to generate phrase-level pitch and duration information for English input. This information is used to annotate the input sentence, which is then processed by the text-to-speech programs currently under development at Bell Labs. In constructing the ,system, our goal has been to test the hypotheses (i) that information available in the syntax tree. in particular. grammatical functions such as subject-predicate and head-complement, is bv itself useful in determining prosodic phrasing for svnthetic speech, and (ii) that it ts possible to use a syntactic parser that specifies grammatical functions to determine prosodic phrasing for synthetic speech. Although certain connections between syntax and prosody are well-known (e.g. the influence of part of speech on stress in words like progress, or the setting off of parenthetical expressions) very little practical knowledge is available on which aspects of syntax might be connected to prosodic phrasing. In many studies, investigators have sought connections between constituent structure and prosody (e.g. Cooper and Paccia-Cooper 1980. Umeda 1982. Gee and Grosjean 1983) but, with the exception of Selkirk (1984). they tend to neglect the representation of grammatical functions in the svntax tree. Moreover, previous work has not been specific enough to provide the basis for a full system implementation. Based on our study of prosodic phrasing in recorded human speech, we Joan Bachenko Eileen Fitzpatrick C. E. Wright AT&T Bell Laboratories Murray Hill, New Jersey 07974 decided to emphasize three aspects of structure that relate to phrasing: syntactic constituency, grammatical function, and constituent length. These findings. which we will discuss in detail, have been implemented as a collection of prosody rules in an experimental text-to-speech system. Two important features characterize our system. First. the input to our prosody system is a parse tree generated by a version of the deterministtc parser Fidditch (Hindle 1983). The left-corner search strategy of this parser and, in particular, its determinism, give Fidditch the speed that makes online text-to-speech production feasible. 1 In building a parse tree, Fldditch identifies the core subject-verb- …

Content truncated to 500 words