| 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
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