VOWELS IN STANDARD AUSTRIAN GERMAN - Acoustics ...

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Vowels in Standard Austrian German
especially F2 changes, do not point to a shift in constriction location, and the concept of
“centralization” does not meet articulatory realism.
3.3. The acoustic-articulatory relationship
Paradoxically, it was also Joos (1948) who pointed at the non-linear relationship
between acoustic output and articulatory adjustments (i.e. different articulatory
adjustments can trigger the same acoustic output). In 1972, Stevens put forward his
widely discussed “quantal theory of speech”. This theory not only gives evidence for
the non-linearity of articulatory-acoustic mapping, but also links these observations to
perception. Stevens (1972, 1989) found three zones – a palatal, a velar and a pharyngeal
zone – , where vowel spectra are relatively insensitive to small displacements in
constriction location, whereas in other regions of the vocal tract, small displacements
render drastical spectral changes. These detected stable areas, which are in good
congruity with the results of Wood (1979), ensure not only a relative stability of the
formant frequencies with respect to displacements in constriction location, but
constrictions in these areas additionally induce a narrow spacing of two spectral peaks,
which – according to Stevens – lead to perceptual enhancement.
For example, the location of constriction for the low vowels is situated in the
lower pharyngeal region. The low vowels strive either for a proximity of F1 and F2 with
a constriction located about 7 – 9 cm from the glottis rendering the back vowel /A/, or
for a proximity of F2 and F3 with a back cavity length of about 4 cm rendering the front
vowels /a, æ/.
For the non-low front vowels, this perceptual enhancement is achieved through
narrow spacing of F2 and F3, or F3 and F4. In varying the length of constriction (5 cm
vs. 6 cm), Stevens in both cases observes
“a broad maximum of F2 for configurations having a back-cavity length in the range 6.5 to 9
cm. In this region where F2 is a maximum, this formant is relatively close to F3. When the
constriction is even farther forward, F3 becomes close to F4, while F2 remains relatively high.