Teza doctorat (pdf) - Universitatea Tehnică

WSEAS TRANSACTIONS ON COMMUNICATIONS Ovidiu Buza, Gavril Toderean
A segment is assumed unvoiced if distance Di
between two adjacent zeros is smaller than a
threshold U:
Di U , i = s,… , s+n (4)
Transient segments are also defined and they
consist of regions for which conditions (2), (3)
and (4) are not accomplished.
After first appliance of above algorithm, a
large set of regions will be created. Since voiced
regions are well determined, the unvoiced are
broken by intercalated silence regions. This
situation appears because unvoiced consonants
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have low amplitude so they can break in many
silence/unvoiced subregions.
Transient segments can also appear inside the
unvoiced segment because of signal bouncing
above zero line.
Figure 7 shows such an example, in which
numbered regions are unvoiced, simple-line and
unnumbered are silence regions, and double-line
are transient regions.
All these regions will be packed together in the
second pass of the algorithm, so the result will be
a single unvoiced region – as one can see in figure
no. 8.
Fig.7. Determining regions for an unvoiced segment of speech
After segmentation, voiced and unvoiced
segments are coupled according to the syllable
chain that is used in vocal database construction
process. Acoustic units are labelled and stored in
database. Each region boundary can be viewed
with a special application and, if necessary, can be
adjusted.
7 Vocal Database Construction
Vocal database includes a subset of Romanian
language syllables. Acoustic units were separated
from male speech and normalized in pitch and
amplitude.
Vocal database with recorded syllables has a
tree data structure. Each node in the tree
corresponds with a syllable characteristic, and a
leaf represents appropriate syllable.
Fig.8. Compacting regions of above segment
Units have been inserted in database following
this classification:
- after length of syllables : we have two, three or
four character syllables (denoted S2, S3 and S4)
and also singular phonemes;
- after position inside the word: initial or median
(Med) and final syllables (Fin);
- after accentuation: stressed or accentuated (A) or
normal (N) syllables.
This classification offers the advantage of
reducing time for matching process between
phonetic and acoustic units.
Organization of vocal database is shown in
figure no. 9. Level one nodes indicate length of
syllables, level two nodes indicate median or final
syllables, and level three accentuated or normal
syllables.