Forensic comparison of ageing voices from automatic and auditory perspectives

Abstract

Comparison of non-contemporary speech samples occurs frequently in forensic speaker-recognition cases. While the ageing-related changes in the voice have been well investigated, the effect of ‘vocal ageing’ on forensic speaker recognition has yet to be fully established. In this article, auditory and automatic experiments providing a deeper insight into the impact of ageing on forensic speaker recognition are presented. A listener test investigating the extent to which vocal ageing is detectable by lay listeners is first presented. A test set of 10 males and 10 females, with recordings spanning approximately 30 years per speaker, are taken from the Trinity College Dublin Speaker Ageing (TCDSA) database. Correct detection of ageing in two samples of the same speaker is found to increase from 64% at a 10-year age difference to 86% at a 30-year age difference. Ageing is significantly more detectable in female speakers than male speakers, and female listeners are significantly better at detecting ageing than male listeners. A link between ageing detectability and speaking fundamental frequency is also observed. A forensic automatic speaker recognition (FASR) experiment with ageing speakers is then presented. Given a test set of five male speakers from the TCDSA database, each with multiple recordings spanning 30–50 years, ageing is shown to progressively weaken the strength-of-evidence (likelihood ratios) of same-speaker comparisons. While there is inter-speaker variability in the extent of the ageing effect, instances of erroneous support for the different-speaker hypothesis are introduced for all speakers within a time-lapse of 10 years. The detrimental effect of ageing on the overall FASR system is also illustrated via Tippett plots.