Masters Degrees (African Languages)

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Browsing Masters Degrees (African Languages) by browse.metadata.advisor "Botha, E. C."

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    Prosodic features of imperatives in Xhosa : implications for a text-to-speech system
    (Stellenbosch : Stellenbosch University, 2000-03) Swart, Philippa H.; Roux, J. C.; Botha, E. C.; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of African Languages.
    ENGLISH ABSTRACT: This study focuses on the prosodic features of imperatives and the role of prosodies in the development of a text-to-speech (TIS) system for Xhosa, an African tone language. The perception of prosody is manifested in suprasegmental features such as fundamental frequency (pitch), intensity (loudness) and duration (length). Very little experimental research has been done on the prosodic features of any grammatical structures (moods and tenses) in Xhosa, therefore it has not yet been determined how and to what degree the different prosodic features are combined and utilized in the production and perception of Xhosa speech. One such grammatical structure, for which no explicit descriptive phonetic information exists, is the imperative mood expressing commands. In this study it was shown how the relationship between duration, pitch and loudness, as manifested in the production and perception of Xhosa imperatives could be determined through acoustic analyses and perceptual experiments. An experimental phonetic approach proved to be essential for the acquisition of substantial and reliable prosodic information. An extensive acoustic analysis was conducted to acquire prosodic information on the production of imperatives by Xhosa mother tongue speakers. Subsequently, various statistical parameters were calculated on the raw acoustic data (i) to establish patterns of significance and (ii) to represent the large amount of numeric data generated, in a compact manner. A perceptual experiment was conducted to investigate the perception of imperatives. The prosodic parameters that were extracted from the acoustic analysis were applied to synthesize imperatives in different contexts. A novel approach to Xhosa speech synthesis was adopted. Monotonous verbs were recorded by one speaker and the pitch and duration of these words were then manipulated with the TD-PSOLA technique. Combining the results of the acoustic analysis and the perceptual experiment made it possible to present a prosodic model for the generation of perceptually acceptable imperati ves in a practical Xhosa TIS system. Prosody generation in a natural language processing (NLP) module and its place within the larger framework of text-to-speech synthesis was discussed. It was shown that existing architectures for TTS synthesis would not be appropriate for Xhosa without some adaptation. Hence, a unique architecture was suggested and its possible application subsequently illustrated. Of particular importance was the development of an alternative algorithm for grapheme-to-phoneme conversion. Keywords: prosody, speech synthesis, speech perception, acoustic analysis, Xhosa