Acoustics of children's speech: Developmental changes of temporal and spectral parameters

Changes in magnitude and variability of duration, fundamental frequency, fo rmant frequencies, and spectral envelope of children's speech are investiga ted as a function of age and gender using data obtained from 436 children, ages 5 to 17 years, and 56 adults. The results confirm that the reduction i n magnitude and within-subject variability of both temporal and spectral ac oustic parameters with age is a major trend associated with speech developm ent in normal children. Between ages 9 and 12, both magnitude and variabili ty of segmental durations decrease significantly and rapidly, converging to adult levels around age 12. Within-subject fundamental frequency and forma nt-frequency variability, however, may reach adult range about 2 or 3 years later. Differentiation of male and female fundamental frequency and forman t frequency patterns begins at around age 11, becoming fully established ar ound age 15. During that time period, changes in vowel formant frequencies of male speakers is approximately linear with age, while such a linear tren d is less obvious for female speakers. These results support the hypothesis of uniform axial growth of the vocal tract for male speakers. The study al so shows evidence for an apparent overshoot in acoustic parameter values, s omewhere between ages 13 and 15, before converging to the canonical levels for adults. For instance, teenagers around age 14 differ from adults in tha t, on average, they show shorter segmental durations and exhibit less withi n-subject variability in durations, fundamental frequency, and spectral env elope measures. (C) 1999 Acoustical Society of America. [S0001-4966(99)0320 2-6].