Strength of forensic voice comparison evidence from the acoustics of filled pauses
DOI:
https://doi.org/10.1558/ijsll.v23i1.29874Keywords:
Forensic voice comparison, hesitation markers, likelihood ratio, formant dynamics, durationsAbstract
This study investigates the evidential value of filled pauses (FPs, i.e. um, uh) as variables in forensic voice comparison. FPs for 60 young male speakers of standard southern British English were analysed, drawn from Task 1 of the DyViS corpus (Nolan et al. 2009). The following acoustic properties were analysed: midpoint frequencies of the first three formants in the vocalic portion; ‘dynamic’ characterisations of formant trajectories (i.e. quadratic polynomial equations fitted to nine measurement points over the entire vowel); vowel duration; and nasal duration for um. Likelihood ratio (LR) scores were computed using the Multivariate Kernel Density formula (MVKD; Aitken and Lucy, 2004) and converted to calibrated log10 LRs (LLRs) using logistic-regression (Brümmer et al., 2007). System validity was assessed using both equal error rate (EER) and the log LR cost function (Cllr; Brümmer and du Preez, 2006). The system with the best performance combines dynamic measurements of all three formants with vowel and nasal duration for um, achieving an EER of 4.08% and Cllr of 0.12. In terms of general patterns, um consistently outperformed uh. For um, the formant dynamic systems generated better validity than those based on midpoints, presumably reflecting the additional degree of formant movement in um caused by the transition from vowel to nasal. By contrast, midpoints outperformed dynamics for the more monophthongal uh. Further, the addition of duration (vowel or vowel and nasal) consistently improved system performance. The study supports the view that FPs have excellent potential as variables in forensic voice comparison cases.References
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Brümmer, N. and du Preez, J. (2006) Application-independent evaluation of speaker detection. Computer Speech and Language 20(2–3): 230–275. http://dx.doi.org/10.1016/j.csl.2005.08.001
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Champod, C. and Evett, I. W. (2000) Commentary on A. P. A. Broeders (1999) ‘Some observations on the use of probability in forensic identification’. Forensic Linguistics 7(2): 238–243.
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Grosjean, F. and Deschamps, A. (1973) Analyse des variables temporelles du français spontané. Phonetica 28(3–4): 191–226. http://dx.doi.org/10.1159/000259456
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Hughes, V. and Foulkes, P. (2015) The relevant population in forensic voice comparison: effects of varying delimitations of social class and age. Speech Communication 66: 218–230. http://dx.doi.org/10.1016/j.specom.2014.10.006
Hughes, V., Wood, S. and Foulkes, P. (forthcoming) Phonetic measurements of hesitations improve the performance of automatic speaker recognition systems.
Jessen, M. (2008) Forensic phonetics. Language and Linguistics Compass 2(4): 671–711. http://dx.doi.org/10.1111/j.1749-818X.2008.00066.x
Jessen, M., Köster, O. and Gfroerer, S. (2005) Influence of vocal effort on average and variability of fundamental frequency. International Journal of Speech, Language and the Law 12(2): 174–213. http://dx.doi.org/10.1558/sll.2005.12.2.174
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Martire, K. A., Kemp, R. I., Sayle, M. and Newell, B. R. (2013) On the interpretation of likelihood ratios in forensic science evidence: presentation formats and the weak evidence effect. Forensic Science International 240: 61–68. http://dx.doi.org/10.1016/j.forsciint.2014.04.005
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Morrison, G. S. (2011b) A comparison of procedures for the calculation of forensic likelihood ratios from acoustic-phonetic data: multivariate kernel density (MVKD) versus Gaussian mixture model-universal background model (GMM-UBM). Speech Communication 53: 242–256.
Morrison, G. S. (2013) Tutorial on logistic-regression calibration and fusion: converting a score to a likelihood ratio. Australian Journal of Forensic Sciences 45(2): 173–197. http://dx.doi.org/10.1080/00450618.2012.733025
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Evett, I. W. (1991) Interpretation: a personal odyssey. In C. G. G. Aitken and D. A. Stone (eds) The Use of Statistics in Forensic Science 9–22. Chichester: Ellis Horwood.
Foulkes, P., Carrol, G. and Hughes, S. (2004) Sociolinguistics and acoustic variability in filled pauses. Paper presented at the annual conference of the International Association for Forensic Phonetics and Acoustics, Helsinki, Finland.
Foulkes, P. and French, J. P. (2012) Forensic speaker comparison: a linguistic-acoustic perspective. In P. M. Tiersma and L. M. Solan (eds) The Oxford Handbook of Language and the Law 557–572. Oxford: Oxford University Press.
Greenberg, S., Carvey, H., Hitchcock, L. and Chang, S. (2003) Temporal properties of spontaneous speech – a syllable-centric perspective. Journal of Phonetics 31(3): 465–485. http://dx.doi.org/10.1016/j.wocn.2003.09.005
Grosjean, F. and Deschamps, A. (1973) Analyse des variables temporelles du français spontané. Phonetica 28(3–4): 191–226. http://dx.doi.org/10.1159/000259456
Hughes, V. (2014) The definition of the relevant population and the collection of data for likelihood ratio-based forensic voice comparison. Unpublished PhD thesis, University of York.
Hughes, V. and Foulkes, P. (2015) The relevant population in forensic voice comparison: effects of varying delimitations of social class and age. Speech Communication 66: 218–230. http://dx.doi.org/10.1016/j.specom.2014.10.006
Hughes, V., Wood, S. and Foulkes, P. (forthcoming) Phonetic measurements of hesitations improve the performance of automatic speaker recognition systems.
Jessen, M. (2008) Forensic phonetics. Language and Linguistics Compass 2(4): 671–711. http://dx.doi.org/10.1111/j.1749-818X.2008.00066.x
Jessen, M., Köster, O. and Gfroerer, S. (2005) Influence of vocal effort on average and variability of fundamental frequency. International Journal of Speech, Language and the Law 12(2): 174–213. http://dx.doi.org/10.1558/sll.2005.12.2.174
Johnson, K. (2012) Acoustic and Auditory Phonetics (3rd edn). Malden, MA: Wiley-Blackwell.
Kendall, T. and Thomas, E. R. (2014) ‘vowels’ (R package). http://cran.r-project.org/web/packages/vowels/index.html
Ketabdar, H. (2004) ‘jEER_DET.m’ (matlab function) (version 1.2 with amendments by Anil Alexander).
Kowal, S., O’Connell, D. C., Forbush, K., Higgins, M., Clarke, L. and D’Anna, K. (1997) Interplay of literacy and orality in inaugural rhetoric. Journal of Psycholinguistic Research 26(1): 1–31. http://dx.doi.org/10.1023/A:1025043620499
Künzel, H. J. (1997) Some general phonetic and forensic aspects of speaking tempo. International Journal of Speech, Language and the Law 4(1): 48–83.
Lennes, M. (2003a) Save_intervals_to_wav_sound_files.praat (Praat script) http://www.helsinki.fi/~lennes/praat-scripts/public/save_intervals_to_wav_sound_files.praat (retrieved 29 July 2013).
Lennes, M. (2003b) Collect_formant_data_from_files.praat. http://www.helsinki.fi/~lennes/praat-scripts/public/collect_formant_data_from_files.praat (retrieved 15 May 2013).
Liberman, M. (2014) UM / UH update. Language Log, 13 December 2014. http://languagelog.ldc.upenn.edu/nll/?p=16414 (and several other posts).
Maclay, H. and Osgood, C. (1959) Hesitation phenomena in spontaneous English speech. Word 15(1): 19–44. http://dx.doi.org/10.1080/00437956.1959.11659682
Martire, K. A., Kemp, R. I., Sayle, M. and Newell, B. R. (2013) On the interpretation of likelihood ratios in forensic science evidence: presentation formats and the weak evidence effect. Forensic Science International 240: 61–68. http://dx.doi.org/10.1016/j.forsciint.2014.04.005
McDougall, K. (2004) Speaker-specific formant dynamics: an experiment on Australian English /a?/. International Journal of Speech, Language and the Law 11(1): 103–130. http://dx.doi.org/10.1558/sll.2004.11.1.103
McDougall, K. (2006) Dynamic features of speech and the characterisation of speakers: towards a new approach using formant frequencies. International Journal of Speech, Language and the Law 13(1): 89–126. http://dx.doi.org/10.1558/sll.2006.13.1.89
McDougall, K. and Nolan, F. (2007) Discrimination of speakers using the formant dynamics of /u?/ in British English. In Proceedings of the 16th International Congress of Phonetic Sciences 1825–1828. Saarbrücken, Germany.
Milroy, L., Milroy, J. and Docherty, G. J. (1994–1997) Phonological Variation and Change in Contemporary British English. Economic and Social Research Council (ESRC) of Great Britain. R000234892.
Morrison, G. S. (2007) matlab implementation of Aitken and Lucy’s (2004) forensic likelihood ratio software using multivariate-kernel-density estimation. http://geoff-morrison.net/#MVKD (retrieved 31 May 2011).
Morrison, G. S. (2009a) Forensic voice comparison and the paradigm shift. Science and Justice 49(4): 298–308.
Morrison, G. S. (2009b) Likelihood-ratio voice comparison using parametric representations of the formant trajectories of diphthongs. Journal of the Acoustical Society of America 125(4): 2387–2397.
Morrison, G. S. (2009c) train_llr_fusion_robust.m (matlab function). http://geoff-morrison.net/#TrainFus (retrieved 13 December 2011).
Morrison, G. S. (2011a) Measuring the validity and reliability of forensic likelihood-ratio systems. Science and Justice 51: 91–98.
Morrison, G. S. (2011b) A comparison of procedures for the calculation of forensic likelihood ratios from acoustic-phonetic data: multivariate kernel density (MVKD) versus Gaussian mixture model-universal background model (GMM-UBM). Speech Communication 53: 242–256.
Morrison, G. S. (2013) Tutorial on logistic-regression calibration and fusion: converting a score to a likelihood ratio. Australian Journal of Forensic Sciences 45(2): 173–197. http://dx.doi.org/10.1080/00450618.2012.733025
Morrison, G. S. (2014) Distinguishing between forensic science and forensic pseudoscience: testing of validity and reliability and approaches to forensic voice comparison. Science and Justice 54(3): 245–256. http://dx.doi.org/10.1016/j.scijus.2013.07.004
Morrison, G. S., Ochoa, F. and Thiruvaran, T. (2012) Database selection for forensic voice comparison. In Proceedings of Odyssey 2012: The Language and Speaker Recognition Workshop 74–77. Singapore.
Morrison, G. S. and Enzinger, E. (2013) Forensic speech science. In N. Nic Daéid (ed.) Proceedings of the 17th International Forensic Science Managers’ Symposium 616–623. Lyon, France.
Mullen, C., Spence, D., Moxey, L., and Jamieson, A. (2014) Perception problems of the verbal scale. Science and Justice 54(2): 154–158. http://dx.doi.org/10.1016/j.scijus.2013.10.004
Nair, B., Alzqhoul, E. and Guillemin, B. J. (2014) Determination of likelihood ratios for forensic voice comparison using principal component analysis. International Journal of Speech Language and the Law 21: 83–112.
Nolan, F. J. (1997) Speaker recognition and forensic phonetics. In W. J. Hardcastle and J. Laver (eds) The Handbook of Phonetic Sciences 744–767. Oxford: Blackwell.
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Published
2016-07-08
Issue
Section
Articles
How to Cite
Hughes, V., Wood, S., & Foulkes, P. (2016). Strength of forensic voice comparison evidence from the acoustics of filled pauses. International Journal of Speech, Language and the Law, 23(1), 99-132. https://doi.org/10.1558/ijsll.v23i1.29874
