Some general phonetic and forensic aspects of speaking tempo

Abstract

The comparability and compatibility of speech samples is of paramount importance to modern techniques of forensic speaker identification. This principle applies also to factors commonly referred to as speaking tempo, speech rate, speed of utterance, and the like, which may differ considerably as a function of various characteristics of the speaking situation. Consider, for example, a blackmailer's telephone call to a victim, i.e. a spontaneous text, often produced in a dialogic situation, and, on the other hand, a text (even the same text) read aloud from a transcript by a suspect and recorded directly over a microphone in a police station. With respect to speaking tempo the compatibility problem is enhanced by the fact that, other than, for instance, F0 and pitch, it cannot be attributed to a single phonetic parameter on the level of either production or perception. In this study the influence of a number of temporal variables which have been associated with speaking tempo in the literature have been investigated in three speaking conditions considered typical of the forensic setting. Furthermore, the potential influence of the telephone recording situation was investigated, a characteristic feature in the vast majority of speaker identification cases. Results from ten speakers and fifteen listeners indicate that speaking condition but not recording condition does in fact have an influence on speaking tempo in terms of both production and perception, with syllable rate, or rather the amount of pausing contained in this parameter, being the best temporal correlate. On the other hand, articulation rate remains almost entirely unaffected and is also remarkably constant within speakers. Therefore it may be regarded as a promising speaker-specific parameter for forensic speaker identification.