(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...