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Sophisticated strategies of voice disguise and their phonetic character
Růžičková, Alžběta ; Bořil, Tomáš (advisor) ; Šturm, Pavel (referee)
Speech contains certain attributes characteristic for a speaker, so-called idiosyncratic features. This thesis focuses on the form of these features in intentional voice disguise - whether speakers are able to change them in a substantial way, or if they tend to remain stable in spite of intentional speech modifications. It was also investigated whether any general tendencies to similar changes of such features under voice disguise exist among the speakers. The observed features were statistical f0 indicators, f0 contours, vowel formants, long- term formant distributions, spectral characteristics of sibilants, intensity, intensity contours, speech and articulation rate, %V and local articulation rate contours. In f0 median and standard deviation, vowel formants, LTFDs, intensity, articulation rate, and %V, prominent shifts under voice disguise were observed in general; in the majority of these parameters, the shifts differed among speakers. However it was found that the value of %V generally tends to rise under voice disguise. Also, intensity showed an increase in majority of cases. In f0 contours, similar patterns were observed among speakers in normal speech, however, in disguised speech, greater differences appeared among speakers; speakers tend to employ nonstandard dynamic f0 patterns more...
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Phonetic manifestations of voice disguise
Růžičková, Alžběta ; Skarnitzl, Radek (advisor) ; Šturm, Pavel (referee)
In forensic practice, when there is the need to identify a speaker using a recording of his speech, forensic voice identification is applied. If the perpetrator is aware of the option of their speech being recorded, for instance in cases such as abduction or blackmail, they can attempt voice disguise in order to thwart voice identification process. This thesis surveys strategies used by Czech speakers, when they attempt to disguise their voices using any means of their choice. Auditory analysis of 80 speakers' disguised voices was performed. 15 of them, who used more complex strategies for disguising their voices, acoustic analysis of fundamental frequency, formant values and speech and articulatory rate was performed. For those speakers, perceptual tests were carried out, to examine the degree of difficulty in uncovering modifications of one's speech and the effect of the used disguise strategies on speaker identifiability in a voice line-up.
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