Age-related changes in long-term average spectra of children's voices.

This paper forms part of a larger study into the nature of singing development in children. The focus here is on an investigation of age-related changes in long-term average spectra (LTAS). Three hundred and twenty children in age groups 4-11 years learned a song. Each child was then digitally recorded singing alone. LTAS curves were calculated from the recordings of each voice and perceived age was estimated by a panel of independent judges. Progressive statistically significant changes were observed in the LTAS as a function of increasing age of the children. These took the form of increases in spectral energy in all frequencies below 5.75 kHz, with concomitant reductions of energy in frequency regions above this point. Increases with age were also found in overall intensity levels of the vocal products. Four experienced listeners audited the voice samples and made estimates of the children's ages. The level of accuracy of age-estimates was remarkably high for children in the youngest age groups, but was reduced with voice samples from older children. Maturation and developing competence of the vocal system, both in growth of lung capacity and at a laryngeal level, are implicated in the generation of age-related spectral changes. Perceived child singer age appears to be less closely related to spectral characteristics (as defined within LTAS) with increasing age of children.