Volume 8, number1 (July 2001)

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Hermann J. Künzel

Beware of the 'telephone effect': the influence of telephone transmission on the measurement of formant frequencies

ABSTRACT 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.
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A. Daniel Yarmey

Earwitness descriptions and speaker identification

ABSTRACT Some 160 men and women selected from public locations agreed to participate in a voice identification experiment. Participants were instructed to listen carefully to the tape-recorded voice of a perpetrator committing a simulated armed robbery of a business establishment. Two minutes later they were asked to describe the voice characteristics of the perpetrator, to recall exactly what he said, and then attempt to identify the speaker from a six-person perpetrator-present or perpetrator-absent voice line-up. Half of the participants in each line-up heard a sample of identical phrases and the other half heard phrases non-identical to those used in the robbery. Accuracy of speaker identification was significantly better than chance; however, there were no significant differences in performance on either line-up as a function of the type of voice sample employed. The confidence-accuracy of identification correlation proved to be non-significant. No significant correlations were found between accuracy of speaker identification and completeness of voice descriptions, or speaker identification and percentage accuracy of recall of actual words used by the perpetrator, or speaker identification and percentage accuracy of recall of idea units contained in the perpetrator’s monologue. It was concluded that voice lineups should be constructed of non-identical phrases rather than the identical phrases reportedly used by the perpetrator.
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Ph.D. abstracts
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Book Reviews

Book reviews
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User: WEIMING LIU
Session: 18888

Forensic Linguistics is published by the University of Birmingham Press.