Out of the Mouths of Babes: Acoustic Variation in Child Speakers
Dr. Sonja Trent-Brown, Hope College
In a classic study, Hillenbrand et al. (1995) conducted an analysis of the acoustic features of American English vowels and published target acoustic descriptions of spectral (pitch) and temporal (duration) features for men, women, and children ages 10-12. Results were presented for “children” and were not broken down for gender, likely because children typically achieve their lower adult voice later in adolescence—age 14 for girls and age 15 for boys. However, there is a gradual lowering of the voice beginning with the onset of puberty, which can begin as early as age 10. As the lowering of the voice occurs, the fundamental frequency (F0)—the characteristic resonance of the vocal tract—is lowered. F0 influences the formant frequencies for the phonological space, which could produce differences across gender, especially for the 11 and 12-year-olds. In addition, no mention was made of speaker ethnic background for either adult or child speakers, and studies have suggested that there is evidence of both perceptual and acoustic variation with respect to speaker ethnicity (Trent-Brown, et al., 2009). Child speakers ages 8-12 were recorded producing words and sentences. Acoustic variation was measured in terms of differences in temporal and spectral acoustic features such as vowel duration, F0, and formant resonance frequencies. A multivariate analysis of variance showed significant differences for both age and gender. For gender, there was a significant F0 variation, with higher values for girls than for boys. For age, F0 varied such that as age increased, fundamental frequency decreased. These findings are in the predicted direction, mirroring adult patterns, suggesting that gender and age are also acoustically important considerations for children.
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