Paramètres pour l'évaluation acoustique de la nasalité. Etude sur une population d'enfants

Abstract
This work deals with the performance of some parameters for evaluating nasality in children with velar impairment. French vowels /a/, /i/ and /u/ have been analysed. We used four types of parameters. First cepstral distances compute the global spectral difference with a reference spectrum for each vowel. Secondly, we studied the linear prediction error. It represents the difference between a spectrum and an all pole spectrum (model of normal vocal tract). More in relation to the nasality and its spectral modifications, we computed the ratio between frequency bands for detecting nasal formants. We have also studied a cepstral distance among the three vowels (nasal distance). This parameter shows the convergence of spectral characteristics to nasal target. It analyses a global phonatory behaviour. In order to study the performance of the parameters, we used the ROC curves (Receptor Operational Characteristics). These curves are plotted for 57 velar impairments and 206 control subjects. The nasal distance gives best results. The efficacy of spectral parameters or LP error changes depending the vowel. Differences between parameters could be explained with knowledge about the nasality.