Judged roughness as a function of formant bandwidth and vowel formant position

The purpose of this study was to investigate the effect of formant bandwidth and vowel formant position on listener perceptions of roughness. Since it is not possible to control human vocal systems, all stimuli for this study were computer derived. An electrical analog of the larynx was used to simulate the glottal source and a series vocal tract analog was used to modify the glottal source to produce vowel-like signals. The vowels /i/, /e/, and /æ/ were selected for investigation because of their physiological and acoustical differences. Three different bandwidth conditions were synthesized for each vowel corresponding to narrow, median, and wide filter settings. All stimuli were recorded on magnetic tape and arranged in an A-B design where every stimulus was paired with every other stimulus. The stimuli were judged by 41 normal hearing listeners, who were instructed to listen to each pair of sounds and to indicate which one in that pair sounded more rough. Results obtained from this study indicate that roughness is greatly influenced by the vowel phonated. Vowels corresponding to high tongue positions and low first formants were judged less rough than vowels characterized by low tongue positions and high first formants. The results also indicate that formant bandwidth is a major contributing factor in perceived judgments of roughness.