Acoustic phonetics of European Portuguese fricative consonants

Abstract

The production of fricatives is not yet fully understood because the mechanism
is particularly complex. Studies of Portuguese fricatives have been very
limited, so in this thesis a novel methodology of corpus design, and temporal
and spectral analysis techniques were developed to enhance our description
of the acoustic properties, and to increase our understanding of the production
of fricatives. The data presented in this thesis could be used to improve
the naturalness of synthetic speech.
Corpora were devised that included the fricatives /f, v, s, z, J, 3/ in the
following contexts: sustained, repeated nonsense words of the form /PV1CV2/,
Portuguese words containing fricatives in frame sentences, and the same set
of words in sentences. Four subjects (two male, two female) were recorded
saying the corpora, using a microphone in the acoustic far - field and a laryngograph.
Temporal analysis of the fricatives revealed a large number of devoiced
examples. Analysis of variance showed that devoicing was significantly
more likely for word-final fricatives and posterior place of articulation.
In addition to the fricatives listed above, we also noticed other fricatives
occurring as allophones of / r , r / in 100 words out of 365. Durations of the
fricative segments were comparable to /R, r / and thus shorter on average
than fricatives / f , v, s, z, J, 3/. Some of the speech segments were continuous
"noisy signals" very similar to those of fricatives. The spectral peak
frequencies of the fricatives occurring in place of / a / were compared to the
other fricatives, which indicated a place of articulation further back than
/J, 3/, and compared to velar and uvular fricative results previously reported
for other languages. These comparisons indicated that the uvular fricatives
[x, k] and the voiceless tapped alveolar [r] were given the phonological role
of /R/ and / r / respectively, though these fricatives have not previously been
reported as phones of standard European Portuguese.
The fricative spectra were parameterised in terms of our knowledge of
the underlying aeroacoustics. The parameters spectral slope, frequency of
maximum amplitude, and dynamic amplitude were developed to characterise
fricative spectra. The parameters behaved as predicted for changes in eSbrt
level, voicing, and location within the fricative. Some combinations were also
useful for separating the fricatives by place or by sibilance.
A preliminary cross - language study of Portuguese and English fricatives
produced by two bilingual siblings is also presented. Although results for
Portuguese and English fricatives seem to be very similar this maybe due
to the use by bilinguals of different production strategies from monolinguals
which attenuate cross - language acoustical contrasts. The English corpus developed
for the bilingual subjects could be used to study monolingual English
speakers.

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