Formant manipulations in voice disguise by mimicry

Abstract

The human voice can be disguised in many ways. The purpose of disguise could either be to impersonate another person, or to conceal the identity of the original speaker, or both. On the other hand, the goal of any biometric analysis on disguised voices could also be twofold: either to find out if the originator of the disguised voice is a given speaker, or to know how a speaker's voice can be manipulated so that the extent and type of disguise that the speaker can perform can be guessed a-priori. Any analysis toward the former goal must rely on the knowledge of what characteristics of a person's voice are least affected or unaffected by attempted disguise. Analysis towards the latter goal must use the knowledge of what sounds are typically most amenable to voluntary variation by the speaker, so that the extent to which given speakers can successfully disguise their voice can be estimated. Our paper attempts to establish a simple methodology for analysis of voice for both goals. We study the voice impersonations performed by an expert mimic, focusing specifically on formants and formant-related measurements, to find out the extent and type of formant manipulations that are performed by the expert at the level of individual phonemes. Expert mimicry is an extreme form of attempted disguise. Our study is presented with the expectation that non-expert attempts at voice disguise by mimicry will fall within the gold standard of manipulation patterns set by an expert mimic, and that it is therefore useful to establish this gold standard.