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Speech Production
Speech Production
Anatomy
The vocal tract may be viewed as a set of
resonating cavities bounded by anatomical
structures which are either fixed or movable.
Acoustics
Sound is generated in several ways and at several
locations in the human vocal tract. The most common sound generation
sources are the quasi-periodic vibration of the
vocal cords and
turbulent noise generated by the passage of air through a narrow
constriction, usually in the oral cavity. More rarely, sounds are
generated by plosive release of air (following the buildup of pressure
behind an obstruction in the vocal tract), implosion (following the
creation of a vacuum behind an obstruction in the vocal tract), and
clicks created by, the action of the tongue pulling away from the roof
of the mouth.
Wherever generated, the sounds underlying speech are relatively
unstructured. For instance, the buzz-like sound of vocal cord
vibration has a relatively simple spectral
properties with harmonics
at frequencies corresponding to integer multiples of the fundamental
frequency. Similarly, friction noise
generated by turbulence has a relatively broad frequency distribution
with a somewhat high pass characteristic.
Despite the simple characteristics of the sound sources used in
speech, the speech signal itself is complexly structured in both
frequency and time. This structure derives from the response characteristics of the vocal tract
with resonances (poles) and anti-resonances (zeroes) located at
frequencies determined by a variety of factors, but primarily the
length and cross-sectional area of the vocal tract above the location
of the sound source. The signal is further structured in time by the
motions of articulators which constantly effects changes in the vocal
tract response characteristics.
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