Índice de variabilidade : um critério de avaliação de parâmetros acústicos de vogais orais e consoantes nasais como elemento para a perícia de comparação de locutores

Abstract

The present research aimed to establish an indicator of variability of acoustic parameters used as elements of confrontation in the expert examination of Voice Comparison. The Variability Index proposed here considers the relationship between intraindividual and interindividual variability and is intended to serve as a reference to determine the advantage of one acoustic parameter over another among those used in Voice Comparison. Besides being obtained from the values of the vowel formants, traditional parameters in the Voice Comparison, the Variability Index was obtained from the nasal consonant formants and from the measurements of vocalic acoustic space and Euclidean Distances between vowels, with the aim to verify the applicability of these parameters in Voice Comparison examination. The stimulus that served as the basis for the study were tonic syllables pronounced in a carrier sentence and the data collection, performed repeatedly in different days and shifts, and aimed at the control of variability, favoring a minimum variability of the acoustic parameters. As for the method, twenty subjects participated in the data collection and the individual average coefficients of variation of the set and general average coefficients of variation of the set served as referents of intraindividual and interindividual variability respectively. As the results of variability, although were not achieved with nasal consonants, suggest that the Variability Index allows us to establish the best parameters to be used in the Voice Comparison. The Index allowed to order the vowels and also supported the proposal that the measurements of vocal acoustic space and Euclidean Distances are possible parameters to be used in Voice Comparison. Unlike Acoustic Phonetics and Articulatory, underlying the research, Articulatory Phonology composes the work as an accessory theoretical contribution in relation to the interpretation of the data of the present doctoral dissertation, but it is understood that it is a valuable theory to explain the linguistic data usually found in forensic practice. The Euclidean Distances between the vertices of the vocalic triangle - [a], [i] and [u] - served to propose an analysis of how the computational implementation of the Task Dynamics model, TADA, treats vowels in a continuously way and consonants as a categorical form.