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Segregation of Concurrent Sounds : II: Effects of Spectral Envelope Tracing, Frequency Modulation Coherence, and Frequency Modulation Width






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Segregation of Concurrent Sounds


II: Effects of Spectral Envelope Tracing, Frequency Modulation Coherence, and Frequency Modulation Width


Marin, Cécile m. h (auteur)
McAdams, Stephen (auteur)





perception et cognition musicales   vocal sound source   vowel synthesis   spectral envelope  


((1)) This study was realized in partial fulfillment of the requirements for C.M.H. Marin's DEA diploma at the Université Paris III (Marin, 1987). The original thesis in French may be obtained by writing to C.M.H. Marin at IRCAM. ((2)) Requests for reprints should be addressed to S. McAdams at the Laboratoire de Psychologie Expérimentale. ((3)) The research presented here concerns the simultaneous grouping of the components of a vocal sound source. McAdams [J. Acoust. Soc. Am. 86, 2148-2159 (1989)] found that when three simultaneous vowels at different pitches were presented with sub-audio frequency modulation, subjects judged them as being more prominent than when no vibrato was present. In a normal voice, when the harmonics of a vowel undergo frequency modulation they also undergo an amplitude modulation which traces the spectral envelope. Our hypothesis was that this spectral tracing could be one of the criteria used by the ear to group components of each vowel, which may help explain the lack of effect of frequency modulation coherence among different vowels in the previous study. In this experiment, two types of vowel synthesis were used in which the component amplitudes of each vowel either remained constant with frequency modulation or traced the spectral envelope. The stimuli for the experiment were chords of three different vowels at pitch intervals of five semitones (ratio 1.33). All the vowels of a given stimulus were produced by the same synthesis method. The subjects' task involved rating the prominence of each vowel in the stimulus. It was assumed that subjects would judge this prominence to be lower when they were not able to distinguish the vowel from the background sound. Also included as stimulus parameters were the different permutations of the three vowels at three pitches and a number of modulation conditions in which vowels were unmodulated, modulated alone, and modulated either coherently with, or independently of, the other vowels. Spectral tracing did not result in increased ratings of vowel prominence compared to stimuli where no spectral tracing was present. It would therefore seem that it has no effect on grouping components of sound sources. Modulated vowels received higher prominence ratings than unmodulated vowels. Vowels modulated alone were judged to be more prominent than vowels modulated with other vowels. There was, however, no significant difference between coherent and independent modulation of the three vowels. Differences among modulation conditions were more marked when the modulation width was 6% than when it was 3%.


Article paru dans : JASA: Journal of the Acoustical Society of America vol. 89 n°1


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2010-02-25 01:00:00

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