An overview of forensic phonetics is presented, focusing on speaker identification as its core task. Speaker profiling/speaker classification is applied when the offender has been recorded, but no suspect has been found. Auditory speaker identification by victims and witnesses becomes relevant when no speech recording of the offender is available. It can take the form of familiar-speaker identification or unfamiliar-speaker identification, and in the latter case a voice line-up/voice parade can be carried out. When recordings of both the offender and a suspect are available, a voice comparison is done by an expert in forensic speech analysis. Current issues and domains in voice comparison analysis include the Bayesian approach to forensic reasoning and the Likelihood Ratio, the use of formant frequency measurements, non-analytic perception and Exemplar Theory, forensic automatic speaker identification, and the interaction between different methods.
Speaker-specific formant dynamics: An experiment on Australian English /aI/
Kirsty McDougall (2004)
Department of Linguistics, University of Cambridge
Formant frequency dynamics are relevant to forensic speaker identification since they are determined by the shape and size of a speaker’s vocal tract and the way he or she configures the articulators for speech. This study investigates individual differences in the formant dynamics of /aI/ produced by five male Australian English speakers, and the effects of changes in speaking rate and prosodic stress on these differences. F1, F2 and F3 frequencies are examined at equidistant time-normalized intervals through /aI/. At each measurement point a degree of speaker individuality is present, and speaker differentiation improves as increasing numbers of measurement points are considered in combination. Patterns of speaker-specific behaviour are generally consistent across different rate-stress conditions. Discriminant analyses based on predictors from all three formants yield classification rates of 88–95%, with nuclear-stressed /aI/ performing best. The findings suggest that further research to develop techniques for characterizing individual speakers using formant dynamics is warranted.
KEYWORDS speaker identity, formant frequency dynamics, diphthongs, speaking
rate, prosodic stress
Beware of the ‘telephone effect’: the influence of telephone transmission on the measurement of formant frequencies
Hermann J. Künzel
Department of Phonetics, University of Marburg
Speech scientists often have to work with speech signals that have been transmitted over the telephone. Although the acoustic properties of telephone transmission such as the band-pass filter characteristics are well known, little attention has been paid to their effect on the measurement of speech parameters.1 This study deals with artefacts introduced by the lower cut-off slope of the transmission channel on vowel formants. For theoretical reasons, frequency components may be assumed to be attenuated the lower they are. Therefore F1 of most vowels can be expected to be affected most. Attenuation of the lower components of a formant will necessarily increase the relative weight of the higher components for the determination of a formant and thus cause an artificial upward shift of its centre frequency. An empirical investigation with directly and telephone-transmitted samples from ten male and ten female subjects shows that the predicted effect on F1 does in fact occur for all tested vowels except /a/, whose F1 is too high to be affected by the slope of the band-pass. The consequences of measurement errors arising from such artefacts are discussed with special reference to speaker identification and empirical dialectology.
KEYWORDS telephone transmission, spectrographic analysis, spectrographic shifting, forensic speaker recognition, dialectologyGörüntülenme: 1033