Forensic speaker comparison of Spanish twins and non-twin siblings: a phonetic-acoustic analysis of formant trajectories in vocalic sequences, glottal source parameters and cepstral characteristics

Abstract

The objective of this thesis is to investigate the phonetic-acoustic similarities and differences in three main speaker groups: monozygotic (MZ) twins, dizygotic (DZ) twins and non-twin siblings. From a forensic-phonetic perspective, the study of this type of speakers is highly relevant, as they represent extreme examples of physical similarity. Distinguishing their voices poses a well-recognized challenge in the forensic realm [see Chapter 2]. Yet, there is an interest in this investigation per se, as the study of genetically identical speakers (MZ twins) and their comparison with non-genetically-identical siblings (DZ twins and non-twin siblings), on the one hand, and with a reference population of unrelated speakers, on the other hand, allows gaining insight into the contribution of nurture and nature in the speech patterns of speakers in general. In other words: to what extent is our voice determined by our DNA and to what extent is it due to educational influences? Besides, this study could be considered the first investigation into the phonetic and acoustic characteristics of Spanish-speaking twins and siblings. According to our research objective, a three-folded approach has been undertaken, as will be described below. For the 54 male speakers recorded ad hoc for this study, three different analyses have been carried out. On the one hand, we have labeled and analyzed the F1-F3 formant trajectories of 19 Spanish vocalic sequences. Secondly, several naturally sustained [e?] tokens have been extracted from the speakers? spontaneous vowel fillers and their glottal source characteristics have been analyzed. These two approaches have been complemented with an automatic speaker recognition analysis carried out with the software Batvox.