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Volume 10, number 2 (December 2003)


CONTENTS

STRENGTH OF FORENSIC SPEAKER IDENTIFICATION EVIDENCE: MULTISPEAKER FORMANT- AND CEPSTRUM-BASED SEGMENTAL DISCRIMINATION WITH A BAYESIAN LIKELIHOOD RATIO AS THRESHOLD

Phil Rose,Takashi Osanaiand Yuko Kinoshita

A forensic-phonetic speaker identification experiment is described which tests to what extent same-speaker pairs from a 60 speaker Japanese data base can be discriminated from different-speaker pairs using a Bayesian likelihood ratio (LR) as discriminant function. Non-contemporaneous telephone recordings are used, with comparison based on mean values from three segments only: a nasal, a voiceless fricative, and a vowel. It is shown that discrimination using the LR-based distance is better than with a conventional distance, and that the cepstrum outperforms the formants. A LR for the test of 50 is obtained for formant-based discrimination, compared to c. 900 for the cepstrum, and the tests are thus shown to be capable of yielding a probative strength of support for the prosecution hypothesis that is conventionally quantified as ‘moderate’ for formants but ‘moderately strong’ for the cepstrum. Comparisons are made with results from similar experiments.

Keywords: forensic speaker identification, strength of evidence, formants, cepstrum


ISSUES IN TRANSCRIPTION: FACTORS AFFECTING THE RELIABILITY OF TRANSCRIPTS AS EVIDENCE IN LEGAL CASES

Helen Fraser

This article considers the reliability of transcripts used as evidence in court, especially transcripts of poor recordings. Background information about human speech and speech perception is presented, and the implications of this information for the use of transcripts of different kinds in legal contexts is considered. Finally, recommendations are made to allow judgement of the reliability of existing transcripts, ensure that newly created transcripts are reliable, and to ensure that transcripts are presented to a jury appropriately.

Keywords: transcription, forensic phonetics, human speech perception, transcript


MASSAGING THE EVIDENCE: THE ‘OVER-WORKING’ OF WITNESS STATEMENTS IN CIVIL CASES

Hugh Tyrwhitt-Drake


This paper considers the process by which witness statements are produced in civil cases. A case study approach is adopted, focussing on an action for defamation that came to trial in Hong Kong. Drawing on a recent judicial report that highlighted the problem of ‘over-working’ in witness statements, the study sets out to ascertain to what extent the phenomenon is the work of lawyers and to what extent it is the work of the witnesses themselves. Fifteen witness statements were analysed to identify areas of textual commonality between the accounts. Striking similarities were found in terms of both formal properties, for example, the layout of the witness statements, and functional properties, for example, verbatim strings across witness statements. Regarding functional properties, it was found that properties that led to apparent divergence, for example, contradictory accounts, were present alongside properties that led to convergence, such as verbatim strings.

Keywords: witness, statements, massaging, over-working, lawyers, civil


A NEW TOOL FOR THE VISUALIZATION OF MAGNETIC FEATURES ON AUDIOTAPES

Dagmar Boss, Stefan Gfroerer, Nikolai Neoustroev


The visualization of magnetic features can be of forensic relevance in the field of tape authentication. The Research Institute for Material Science and Technology in Zelenograd, Russia, has developed crystals with magneto-optical properties which permit convenient, precise and non-destructive visualization of magnetic information. These crystals change their optical properties according to external magnetic fields. The magneto-optical effects may be used for developing images of the magnetic structure of any analogue or digital recording. In this paper, we first provide some theoretical background about several magneto-optical effects. Subsequently, two experiments on visualization effects that are based on different physical principles (Kerr Effect, Faraday Effect) are described. Selected forensically relevant features detected on analogue recordings are shown. Special emphasis is given to visual features that may be used for authentication purposes

Keywords: tape authentication, visualization, magnetic features, magneto-optical


CASE REPORT: A RECENT VOICE PARADE

Francis Nolan


BOOK REVIEWS

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西北政法大学外国语学院刘蔚铭教授创建与维护

2002-05-062008-01-25