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An algorithm for automatic segmentation of speech
signals into syllables: a comparison between Italian
and Castillan results
Cutugno, Francesco; Origlia, Antonio
LUSI-Lab@Dipartimento di Scienze Fisiche - Università di Napoli "Federico II" - Italia
In this paper we present an algorithm for speech syllabification using an
approach which is purely deterministic and language and content independent.
Following a research line concerning the investigation about the role of
intensity temporal patterns (Petrillo&Cutugno 2003) we show here a rule based
system using as features: a)the position of the most relevant energy maxima, b)
harmonicity measurements, c) syllable nuclei detection,d) fine marker
positioning strategies.
Central to the algorithm is the analysis of the energy temporal profile which is
obtained by shifting a window on the speech signal every 10 ms and smoothing
the derived pattern with a 45 ms Gaussian window. The obtained pattern will
include a series of maxima among which we have to run a decision process to
select proper nuclei candidates. This choice is based on the combined analysis
of the slope of the energy rise and the height of the following energy valley and
of the data derived by the Harmonicity analysis.
Syllable boundaries are then placed at the energy minima between consecutive
syllable nuclei candidates available at the end of the selection process.
However there are several cases in which this process requires some attention:
in order to cover all cases, the syllable boundary is set corresponding to the
minimum value of the energy derivative between the previous syllable nucleus
and the current energy minimum.
The algorithm is implemented as a Praat Script and it is possible to use it in a
batch procedure in order to process large speech corpora. The script is freely
available for research purposes.
The tool has been tested on two corpora, one for Italian for which an accurate
manual labeling at phone level is available and one for Spanish Castillan. The
Italian speech corpus is CLIPS (Corpora e Lessici di Italiano Parlato e Scritto -
Savy&Cutugno 2008) while the Spanish one is SES (Spanish Emotional
Speech - Montero et al. 1998).
The evaluation of the two automatic segmentation was performed using a
modified version of Petek's algorithm (Petek,1996) which compares a series of
temporal markers produced by a manual segmentation process with the
automatically obtained one. Errors are expressed in terms of misplacement,
insertion and deletion. Misplacements are considered as substitution of a
correct marker with a wrong one if the absolute distance between the two is
greater than a fixed threshold.
Results on CLIPS for Italian are the following: Substitutions 2.9%, Deletions
10.2%, Insertions 7.4% with a final accuracy of 79.5%.
Insertion and Deletion errors are respectively in connection with the
phenomenon of syllable Split in presence of particularly long nuclei, and
Coupling which occur when a consonantal onset in a given syllable is lenited
and consequently the usual features indicating a sonority valley are missing. An
accurate description of this phenomenon will be offered in the paper. In
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