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

TLDR

The study investigates how the magnitude and variability of temporal and spectral acoustic parameters in children’s speech change with age and gender. It analyzes recordings from 436 children aged 5–17 and 56 adults, measuring duration, fundamental frequency, formant frequencies, and spectral envelope. Results show a progressive reduction in magnitude and variability of both temporal and spectral parameters, with segmental durations reaching adult levels by age 12, fundamental frequency and formant variability by 14–15, gender differentiation emerging around 11–15, male vowel formants following a linear age trend supporting uniform axial growth, and a transient overshoot of acoustic values between ages 13–15 before converging to adult norms.

Abstract

Changes in magnitude and variability of duration, fundamental frequency, formant frequencies, and spectral envelope of children's speech are investigated 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 in magnitude and within-subject variability of both temporal and spectral acoustic parameters with age is a major trend associated with speech development in normal children. Between ages 9 and 12, both magnitude and variability of segmental durations decrease significantly and rapidly, converging to adult levels around age 12. Within-subject fundamental frequency and formant-frequency variability, however, may reach adult range about 2 or 3 years later. Differentiation of male and female fundamental frequency and formant frequency patterns begins at around age 11, becoming fully established around age 15. During that time period, changes in vowel formant frequencies of male speakers is approximately linear with age, while such a linear trend is less obvious for female speakers. These results support the hypothesis of uniform axial growth of the vocal tract for male speakers. The study also shows evidence for an apparent overshoot in acoustic parameter values, somewhere between ages 13 and 15, before converging to the canonical levels for adults. For instance, teenagers around age 14 differ from adults in that, on average, they show shorter segmental durations and exhibit less within-subject variability in durations, fundamental frequency, and spectral envelope measures.