title: Euclidean Distances as measures of speaker similarity including identical twin pairs: A forensic investigation using source and filter voice characteristics.
abstract: There is a growing consensus that hybrid approaches are necessary for successful speaker characterization in Forensic Speaker Comparison (FSC); hence this study explores the forensic potential of voice features combining source and filter characteristics. The former relate to the action of the vocal folds while the latter reflect the geometry of the speaker's vocal tract. This set of features have been extracted from pause fillers, which are long enough for robust feature estimation while spontaneous enough to be extracted from voice samples in real forensic casework. Speaker similarity was measured using standardized Euclidean Distances (ED) between pairs of speakers: 54 different-speaker (DS) comparisons, 54 same-speaker (SS) comparisons and 12 comparisons between monozygotic twins (MZ). Results revealed that the differences between DS and SS comparisons were significant in both high quality and telephone-filtered recordings, with no false rejections and limited false acceptances; this finding suggests that this set of voice features is highly speaker-dependent and therefore forensically useful. Mean ED for MZ pairs lies between the average ED for SS comparisons and DS comparisons, as expected according to the literature on twin voices. Specific cases of MZ speakers with very high ED (i.e. strong dissimilarity) are discussed in the context of sociophonetic and twin studies. A preliminary simplification of the Vocal Profile Analysis (VPA) Scheme is proposed, which enables the quantification of voice quality features in the perceptual assessment of speaker similarity, and allows for the calculation of perceptual-acoustic correlations. The adequacy of z-score normalization for this study is also discussed, as well as the relevance of heat maps for detecting the so-called phantoms in recent approaches to the biometric menagerie.
authors.affiliation: Department of Language and Linguistic Science, University of York, Heslington, York, YO10 5DD, UK. Electronic address: eugenia.sansegundo@york.ac.uk.
authors.forename: Eugenia
authors.initials: E
authors.lastname: San Segundo
authors.affiliation: Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, UK; Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Oxford, UK; Sleep and Circadian Neuroscience Institute, Nuffield Department of Medicine, University of Oxford, UK. Electronic address: tsanas@maths.ox.ac.uk.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Tsanas
authors.affiliation: NeuVox Lab, Center for Biomedical Technology, Universidad Politécnica de Madrid, Madrid, Spain. Electronic address: pedro@fi.upm.es.
authors.forename: Pedro
authors.initials: P
authors.lastname: Gómez-Vilda
mesh_terms: D044707:Forensic Sciences; D006801:Humans; D015233:Models, Statistical; D010700:Phonetics; D013061:Speech Acoustics; D014430:Twins, Monozygotic; D014831:Voice; D014833:Voice Quality
keywords: Acoustic analysis; Forensic phonetics; Pause fillers; Perceptual assessment; Twins; Voice quality