A method for generating natural-sounding speech stimuli for cognitive brain research

Objective: In response to the rapidly increasing interest in using human vo ice in cognitive brain research, a new method, semisynthetic speech generat ion (SSG), is presented for generation of speech stimuli. Methods: The method synthesizes speech stimuli as a combination of purely a rtificial processes and processes that originate from the natural human spe ech production mechanism. SSG first estimates the source of speech, the glo ttal flow, from a natural utterance using an inverse filtering technique. T he glottal flow obtained is then used as an excitation to an artificial dig ital filter that models the formant structure of speech. Results: SSG is superior to commercial voice synthesizers because it yields speech stimuli of a highly natural quality due to the contribution of the man-originating glottal excitation. Conclusion: The artificial modelling of the vocal tract enables one to adju st the formant frequencies of the stimuli as desired, thus making SSG suita ble for cognitive experiments using speech sounds as stimuli. (C) 1999 Else vier Science Ireland Ltd. All rights reserved.