Normal voice in children between 6 and 12 years of age: database and nonlinear analysis

This study was carried out using a transversal design. It aimed to investigate possible changes of the normal voice in children before mutation, to create a database for the parameters used in the study, and to examine the use of fractal dimension and the largest Lyapunov exponent (LLE) in the assessment of nonpathological phenomena. Two hundred twelve children were enrolled: 111 females and 101 males; and 9 six-year-olds, 24 seven-year-olds, 18 eight-year-olds, 25 nine-year-olds, 27 ten-year-olds, 55 eleven-year-olds, and 54 twelve-year-olds. Fundamental frequency (Fo) decreased with age and was lower in boys than in girls. Jitter and shimmer did not significantly differ with age or gender. Fractal dimension and LLE were significantly lower in boys; LLE decreased with age. The present series confirmed the established findings that Fo is lower in boys than in girls, even before mutation, and decreases with age; two other classical voice analysis parameters, jitter and shimmer, also showed the same behavior as described in the literature. The study of nonlinear parameters (fractal dimension and LLE) showed that laryngeal dynamics is more stable in boys than in girls, and that stability is correlated with age.