Correlation between vocal tract length, body height, formant frequencies, and pitch frequency for the five Japanese vowels uttered by fifteen male speakers

We conducted quantitative analyses of a magnetic resonance imaging (MRI) database to examine the correlation between physical measures (vocal tract length and body height) and acoustic parameters (pitch and formant frequencies) of vowels. The vocal tract length was measured from MRI data for the five Japanese vowels produced by fifteen male Japanese speakers between the ages of 24 and 55. The acoustic features were computed from vowel sounds recorded during scan. The vocal tract length showed a weak positive correlation with the speakers’ age (correlation coefficient r = 0.51) but not with the speaker body height (r = 0.08). There were only weaker correlations between the vocal tract length and the first four formant frequencies except that F1 and F2 of the vowel /e/ show negative correlations with the vocal tract length (F1: r = -0.65, F2: r = -0.56). The result suggests that the vocal tract length is one of the dominant factors causing individual differences in the formant frequencies for the vowel /e/, produced by not forming a strong constriction. Furthermore, the pitch frequency was negatively correlated with the body height (r = -0.61).