Parametric representations of the formant trajectories of Spanish vocalic sequences for likelihood-ratio-based forensic voice comparison

Abstract

Non-contemporaneous speech samples from 30 Spanish male speakers were compared within the forensic-likelihood-ratio framework. The acoustic parameters studied were the formant trajectories of a series of vocalic sequences (pronounced as diphthongs /we/ /je/, and in hiatus /ia/ /ai/) in order to analyze their suitability for forensic voice comparison. Following Morrison [J. Acoust. Soc. Am. 119, 2387-2397 (2009)], parametric curves (polynomials and discrete cosine transforms) were fitted to these formant trajectories. The estimated coefficient values from the parametric curves were used as input to a multivariate-kernel-density formula for calculating likelihood ratios expressing the probability of obtaining the observed differences between two speech samples under two opposing hypothesis: that the samples were produced by the same speaker and that the samples were produced by different speakers. Cross-validated likelihood-ratio results from systems based on different parametric curves were calibrated and evaluated using the log-likelihood-ratio-cost function (Cllr). The cross-validated likelihood ratios from the best-performing system for each vocalic sequence were fused using logistic regression