Vowel normalization using stop consonant loci.
Christian Koops · The Journal of the Acoustical Society of America · 2009
Vowel normalization techniques used in sociophonetics aim to eliminate the influence of vocal tract length differences on resonant frequencies so that speaker-specific vowel configurations can be compared more precisely. In vowel-extrinsic methods, a speaker’s F1-F2 range is scaled up or down, and vowel spaces are aligned using the geometrical F1-F2 mean. However, a speaker’s F1-F2 mean may be systematically biased if his or her vowel configuration is affected by a set of parallel vowel shifts, e.g., fronting or raising of several vowels in a chain shift. To address this problem, an alternative method of deriving speaker-specific scaling factors was tested based on a vowel-independent acoustic measure: the locus (virtual origin) of the second formant transition following the /d/-release. Forty adult speakers of American English (20 male, 20 female) were recorded reading ten repetitions of 16 /dVd/-words. From these data, individual F1-F2 means and locus equations were calculated, including each speaker’s F2 locus frequency for /d/. Preliminary results based on the corner vowels /i, a, u/ show that F2 locus and F1-F2 mean are strongly correlated (r-squared=0.84). Statistical modeling is underway to determine whether scaling factors derived from locus analysis are superior to scaling factors derived from F1-F2 means.