Acoustic analysis of aperiodic voice: perturbation and nonlinear dynamic properties in esophageal phonation.

Esophageal voice is a method of voice production after total laryngectomy. Previous research suggests that perturbation analysis may inaccurately measure aperiodic voices and that nonlinear dynamic methods may be more appropriate for analyzing signals of this type. Therefore, we hypothesized that nonlinear dynamic analysis would be more capable than perturbation parameters for reliable measurement of the aperiodic esophageal voice. The study design was acoustic comparison of esophageal and normal voice cohorts using nonlinear dynamic and perturbation measures. Twenty subjects in two age-matched groups participated in the study. Jitter, shimmer, signal-to-noise ratio (SNR), correlation dimension, and second-order entropy were measured from audio recordings of subjects' voices. Jitter and shimmer values were significantly higher and SNR values were significantly lower for esophageal voices than for normal voices. Error (err) count values, which indicate perturbation analysis reliability, were 0 in normal voices and significantly higher in esophageal voices. Error was attributable to signal aperiodicity and demonstrated that perturbation analysis yielded questionable results for esophageal voice. However, nonlinear dynamics measures analyzed both cohorts reliably and indicated that esophageal voice was significantly more chaotic than normal voice. The results demonstrated the capability of nonlinear dynamic methods to reliably quantify both aperiodic and periodic signals and differentiate normal from esophageal voices. It is suggested that nonlinear dynamic analysis be used preferentially for acoustic characterization of aperiodic voices, such as esophageal voice. Future research should focus on clarification of perturbation analysis reliability and further application of nonlinear dynamic measures to aperiodic voices.