The effects of speaker individuality on voice disguise and speaker recognition in application to forensic speech science

人类的声音被广泛认为是一个重要的身份标志，将一个人固定在他们的身体上。假设个体声音的独特性是法医语言科学研究的基础，法医语言科学是应用语言科学的一个领域，致力于在刑事调查中使用声音证据。典型的法医案件工作包括确定两个录音是否可能来自同一说话人，或者它们是否可能由不同的说话人产生（Nolan, 1991）。一个对这项任务提出重大挑战的领域是声音伪装，即一个人有目的地改变自己的声音，使其听起来像别人，从而逃避识别。这在身份欺诈检测实例的背景下尤其重要（特别是在银行和其他大型组织实施语音识别技术的当前环境中），过去一年的总体欺诈案件增加了15%（国家统计局，2019年）。令人担忧的是，过去的研究发现，一些人可以模仿他人的言语，准确度很高（Leemann & Kolly, 2015）。尽管如此，迄今为止的研究还没有全面解决声音伪装的精确机制，以及即使是最好的伪装是否包含可以识别说话者的特征。因此，要对伪装的声音是否可能是嫌疑人提供一个强有力的结论可能是极其困难的，因为必须提供来自语音信号的具体证据才能在法庭上证明这种主张是合理的。

The human voice is widely viewed as an important marker of identity, anchoring an individual to their body. The hypothesised uniqueness of individual voices lies at the foundation of research in forensic speech science, which is an area of applied speech science dedicated to the use of voice evidence in criminal investigations. Typical forensic casework involves establishing whether or not two voice recordings are likely to be from the same speaker, or whether they could have been produced by different speakers (Nolan, 1991). One area that provides a significant challenge to this task is vocal disguise, whereby an individual has purposefully modified their voice in order to sound like somebody else and, therefore, evade identification. This is particularly relevant in the context of3detecting instances of identity fraud (especially in the current climate of voice identification technologies implemented by banks and other large organisations), with an increase of 15% in the past year of overall fraud cases (Office of National Statistics, 2019). Worryingly, past research has found that some individuals can imitate the speech of others to a high degree of accuracy (Leemann & Kolly, 2015). Despite this, research to date has not comprehensively addressed the precise mechanisms of voice disguise and whether even the best disguises contain features that could identify the speaker. As a consequence, it can be extremely difficult to provide a robust conclusion on whether a disguised voice is likely to be the suspect or not, as specific evidence from the speech signal must be presented in order to justify such claims in court.