Effects of selected vocal disguises upon spectrographic speaker identification

This research was designed to investigate the effects of selected vocal disguises upon spectrographic speaker identification. The experiment consisted of open-trial, spectrogram-matching tasks with 15 “reference” and 15 “matching” speakers. The speakers produced two sentence sets in six different ways: (1) normal speaking mode, (2) old-age disguise, (3) hoarse disguise, (4) hypernasal disguise, (5) slow-rate disguise, and (6) free disguise of his own choosing. The reference spectrograms were always undisguised speech samples; the matching spectrograms were either disguised or undisguised. Four trained spectrographic examiners completed the matching tasks. The results revealed that the examiners were able to match speakers with a moderate degree of accuracy (56.67% correct) when there was no attempt to vocally disguise either utterance. The inclusion of disguised speech samples in the matching tasks significantly interfered with speaker-identification performance. However, certain voice disguises were more effective than others. In addition, certain speakers were considerably more difficult to identify than others. The examiners exhibited poor test-retest reliability for the undisguised tasks. In summary, this investigation did not substantiate prior claims that spectrographic speaker identification is unaffected by attempts at disguising one's voice.