Voice Comparison and Rhythm: Behavioral Differences between Target and Non-target Comparisons

Abstract

It is common to see voice recordings being presented as a forensic trace in court. Generally, a forensic expert is asked to analyze both suspect and criminal's voice samples in order to indicate whether the evidence supports the prosecution (same-speaker) or defence (different-speakers) hypotheses. This process is known as Forensic Voice Comparison (FVC). Since the emergence of the DNA typing model, the likelihood-ratio (LR) framework has become the golden standard in forensic sciences. The LR not only supports one of the hypotheses but also quantifies the strength of its support. However, the LR accepts some practical limitations due to its estimation process itself. It is particularly true when Automatic Speaker Recognition (ASpR) systems are considered as they are outputting a score in all situations regardless of the case specific conditions. Indeed, several factors are not taken into account by the estimation process like the quality and quantity of information in both voice recordings , their phonological content or also the speakers intrinsic characteristics. In our recent study, we showed the importance of the phonemic content and we highlighted interesting differences between inter-speakers effects and intra-speaker's ones. In this article, we wish to take our previous analysis a step farther and investigate the impact of rhythm variation separately on target and non-target trials.