Developmental variability in voice quality: acoustic reference data from 275 children aged 5–12 years

Background: Sound prolongation tasks are commonly employed to evaluate voice quality (Fang-Ling & Matteson, 2014). However, variability in children’s performance and limited norms, especially across diverse populations, pose significant challenges for clinicians in accurately interpreting performances. This study examined voice quality and variability in sound prolongation tasks among 275 Scottish children aged 5;0–11;9 years, determining comprehensive acoustic reference data in primary school aged children.
Method: Participants produced sustained phonations of /a/, /s/, and /z/ to assess respiratory and phonatory performance. Duration measures and acoustic parameters including jitter, shimmer, Harmonics-to-Noise Ratio (HNR), Cepstral Peak Prominence (CPP), and the s/z ratio were analysed in terms of age and sex to explore developmental trends and variability in respiratory and phonatory control.
Results: There were significant age-related increases in sound prolongation durations, with older children (7-12 years) outperforming younger peers (5–6 years), reflecting more mature respiratory and vocal fold control. In terms of voice quality, CPP values were significantly higher in older children, indicating improved vocal stability and harmonic richness, while jitter, shimmer, and HNR remained consistent across age groups. Age-related changes in the s/z ratio were also observed, underscoring developmental changes in phonatory-respiratory coordination. Individual variability pertaining to all measures was prominent, particularly among older children. No significant sex differences were observed, except for the s/z ratio, where females demonstrated higher values.
Conclusion: The findings highlight the clear developmental trajectories for the respiratory and phonatory subsystems of speech. Additionally, the reference norms provide a critical resource for clinicians, offering age- and sex-specific acoustic reference data for children’s voice quality measures. The study further highlights the importance of accounting for developmental variability and comprehensive approaches to assessing voice quality to support the diagnosis of voice disorders in children.