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The effect of education on the ability to disguise one's voice
Vyhnálková, Lenka ; Skarnitzl, Radek (advisor) ; Machač, Pavel (referee)
(in English): Voice disguise can potentially occur in every utterance that is associated with any criminal case. In order to identify the perpetrator it is necessary to analyze the speech and understand how the different types of voice disguise can affect the speaker's voice qualities. This thesis focuses on the ability of voice disguise, portraying three groups of speakers in relation to their educational background. The aim of this work is to determine the strategies adopted by the speaker to conceal his/her identity and furthermore it poses the question whether differences among the three groups of speakers, their choice of strategy and its inherent success can be found. The basis for this research stems from 86 recordings which were undertaken in Pilsen and Prague with 43 young people aged 20 to 31. Two read utterances, one undisguised and the other freely disguised, were obtained from each of the participants and were compared with each other. The results show that the preferred forms of voice disguise appeared to involve changes in phonation - especially decrease or increase of fundamental frequency of the speaker's voice. Among the three groups of speakers, their choice and the success of the chosen strategy only minor differences could be found, yet for a final confirmation of this...
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Spectral properties of the source signal as speaker-specific cues
Vaňková, Jitka ; Skarnitzl, Radek (advisor) ; Volín, Jan (referee)
Despite a continuous development in computer sciences and related disciplines, speaker identification remains one of the most challenging tasks in forensic phonetics. The reason for this is the fact that our knowledge of how identity is reflected in the acoustic signal is still limited. The present study aims to contribute to the search of speaker-specific cues by examining spectral properties of the source signal. Specifically, it examines to what extent three short-term measures of spectral tilt, namely H1-H2, H1-A1 and H1-A3, can discriminate 16 Czech female speakers. It also addresses the influence of vowel quality, syllable status with respect to stress and position of stress group in the utterance on the values of these measures. The results show that these parameters do have some discriminative power, though the contribution of individual parameters differs. The study indicates that discrimination of speakers is the most successful in stressed syllables and argues that individual vowels could differ in their usefulness for speaker identification. The results of LDA based on these short- term measures of spectral tilt were complemented with long-term measures, namely alpha index, Kitzing index and Hammarberg index which quantify the slope of the LTAS. The present study suggests that...
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Speaker identity indicators in the domain of the temporal modulation of the speech signal
Weingartová, Lenka ; Volín, Jan (advisor) ; Machač, Pavel (referee)
AbstractAbstractAbstractAbstract This diploma thesis aims to contribute to the field of speaker recognition in the domain of temporal changes in the speech signal. After a brief introduction into forensic phonetics, it gives an outline of approaches and factors which help or hinder successful recognition. The focus is then shifted to the temporal structure of speech and approaches to its analysis currently in use. The practical section of this thesis consists of an experiment designed to assess the contribution of certain temporal measures to speaker recognition. The variables used here are %V (the proportion of vocalic intervals within a sentence), ΔV and ΔC (the standard deviation of the duration of vocalic/consonantal intervals within a sentence), VarcoV and VarcoC (the previous variables normalised for average interval duration) and the Pairwise Variability Indices, both vocalic and consonantal, raw and normalised. Beside these, another variable is used to capture the local articulation rate and especially final deceleration in the utterances - LAR (the inverse of the distance between successive midpoints of the vocalic intervals). Whereas the first mentioned variables are not very successful in distinguishing the speakers, LAR seems very well suited for capturing speaker idiosyncrasies, although...
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