The study of Portuguese fricatives is a complex problem, which has not been explored fully. As part of a larger study of the acoustic properties of Portuguese fricatives, a corpus based on 154 Portuguese words containing the fricatives /f, v, s, z, ʃ, ʒ/ in combination with the non-nasal vowels /i, ɨ, e, ɛ, ɐ, a, ɔ, o, u/ has been recorded. A nonsense word corpus was also devised consisting of /pVCV/ sequences. Sustained Portuguese fricative consonants were also recorded. Both the acoustic speech signal and the laryngograph signal were recorded in a sound treated booth. Observation of laryngograph and acoustic signals of Portuguese words has revealed that there is a large number of devoiced examples. Averaged power spectra were computed for all fricatives. For the nonsense word corpus, ensemble averaging based on one DFT computed at the same event in each of nine tokens was used. For all other corpora, time averaging of DFTs computed from nine 10ms windows was used. Substantial differences are found between spectra of voiced and unvoiced, same-place fricatives. Other comparisons of effort level in sustained fricatives to position in the word add to a knowledge of the interaction of voice and frication source in Portuguese.
The multiple comparisons possible in such a study, across speakers, corpora, place, vowel context, syllable stress, location within fricative, etc., demanded a systematic approach, since our interest is primarily in the production mechanisms of the fricatives and the language-specific variation of these mechanisms. We sought a way of parameterizing the fricatives that makes use of our knowledge of the underlying aeroacoustics. The parameters spectral slope, frequency of maximum amplitude, and dynamic amplitude, were developed to characterize fricative spectra, and applied to corpora. The parameters behaved as predicted for changes in effort level, voicing, and location within the fricative. Some combinations were also useful for separating the fricatives by place or by sibilance.
The work presented in this Thesis, is a systematic study of European Portuguese fricatives in a range of contexts, with temporal and spectral analysis. Our long-range goal is synthesis of Portuguese fricatives.
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