Likelihood Ratio-based Forensic Voice Comparison on L2 speakers: A Case of Hong Kong native male production of English vowels

This study is a pilot research that explores the effectiveness of a likelihood ratio (LR)-based forensic voice comparison (FVC) system built on non-native speech production. More spe-cifically, it looks at native Hong Kong Can-tonese-speaking male productions of English vowels, and the extent to which FVC can work on these speakers. 15 speakers partici-pated in the research, involving two non-contemporaneous recording sessions with six predetermined target words – “hello”, “bye”, “left”, “right”, “yes”, and “no”. Formant fre-quency values were measured from the trajec-tories of the vowels and surrounding segments. These trajectories were modelled using discrete cosine transforms for each for-mant (F1, F2 and F3), and the coefficient val-ues were used as feature vectors in the LR calculations. LRs were calculated using the multivariate-kernel-density method. The re-sults are reported along two metrics of per-formance, namely the log-likelihood-ratio cost and 95 % credible intervals. The six best-performing word-specific outputs are present-ed and compared. We find that FVC can be built using L2 speech production, and the re-sults are comparable to similar systems built on native speech.