A likelihood ratio-based forensic voice comparison using formant trajectories of Thai diphthongs

Abstract

This study investigates the phonetic–acoustic properties of the three Thai diphthongs /i:a, ī:a, u:a/ within the context of forensic voice comparison. The likelihood-ratio approach is applied to the parameterized formant trajectories of each diphthong in order to evaluate their respective discriminatory power. The aim of this study is to assess to what extent such properties can be used to distinguish, in a probabilistic sense, two or more speech samples. Formant trajectories were fitted using both polynomial interpolation and the discrete cosine transform. Likelihood ratio values were derived by the multivariate kernel density (MVKD) estimation approach proposed by Aitken and Lucy (2004) and then calibrated by using the log-likelihood ratio cost function—Cllr (Brummer 2005) and the 95%-credible interval (Morrison et al., 2010). We have finished gathering all speech data for this study, and are currently processing the data using various computational tools.