Multi-parametric analysis of speech timing in inter-talker identical twin pairs and cross-pair comparisons: Some forensic implications

Abstract

The purpose of this study was to assess the speaker-discriminatory potential of a set of speech timing parameters while probing their suitability for forensic speaker comparison applications. The recordings comprised of spontaneous dialogues between twin pairs through mobile phones while being directly recorded with professional headset microphones. Speaker comparisons were performed with twins speakers engaged in a dialogue (i.e., intra-twin pairs) and among all subjects (i.e., cross-twin pairs). The participants were 20 Brazilian Portuguese speakers, ten male identical twin pairs from the same dialectal area. A set of 11 speech timing parameters was extracted and analyzed, including speech rate, articulation rate, syllable duration (V-V unit), vowel duration, and pause duration. Three system performance estimates were considered for assessing the suitability of the parameters for speaker comparison purposes, namely global Cllr, EER, and AUC values. These were interpreted while also taking into consideration the analysis of effect sizes. Overall, speech rate and articulation rate were found the most reliable parameters, displaying the largest effect sizes for the factor “speaker” and the best system performance outcomes, namely lowest Cllr, EER, and highest AUC values. Conversely, smaller effect sizes were found for the other parameters, which is compatible with a lower explanatory potential of the speaker identity on the duration of such units and a possibly higher linguistic control regarding their temporal variation. In addition, there was a tendency for speech timing estimates based on larger temporal intervals to present larger effect sizes and better speaker-discriminatory performance. Finally, identical twin pairs were found remarkably similar in their speech temporal patterns at the macro and micro levels while engaging in a dialogue, resulting in poor system discriminatory performance. Possible underlying factors for such a striking convergence in identical twins’ speech timing patterns are presented and discussed.

Assessing the speaker discriminatory power asymmetry of different acoustic-phonetic parameters

“…When comparing previous analyses with data from Brazilian Portuguese [4,5], a relatively similar pattern was also suggested, in which speech temporal parameters performed worse compared to melodic estimates, as revealed by the discrepancy in Cllr and EER values.…”

“…Overall, six acoustic-phonetic parameters were chosen for the comparison based on their relatively better discriminatory performance in relation to other parameters of the same category assessed in previous studies, cf. [4,5,7]. The Praat script "ProsodyDescriptorExtractor" [8] was used for the extractions:…”

On the speaker discriminatory power asymmetry regarding acoustic-phonetic parameters and the impact of speaking style

“…It should also be acknowledged that, as previous studies suggest, cf. Heuvel ( 1996 ) and Cavalcanti et al ( 2022 ), an uneven level of speaker specificity appears to be present within the speech temporal domain itself. In Cavalcanti et al ( 2022 ), for instance, it was observed that macro speech timing parameters (e.g., speech and articulation rates) appeared to contain more speaker-specific information in relation to micro speech timing parameters (e.g., vowel and syllable duration).…”

“…Heuvel ( 1996 ) and Cavalcanti et al ( 2022 ), an uneven level of speaker specificity appears to be present within the speech temporal domain itself. In Cavalcanti et al ( 2022 ), for instance, it was observed that macro speech timing parameters (e.g., speech and articulation rates) appeared to contain more speaker-specific information in relation to micro speech timing parameters (e.g., vowel and syllable duration). According to the arguments presented in that paper, a low explanatory potential of the speaker identity regarding micro-temporal parameters may suggest those units as under a higher level of linguistic control.…”