CENTER OF GRAVITY EFFECT IN VOWEL SPECTRA AND CRITICAL DISTANCE BETWEEN THE FORMANTS - PSYCHO-ACOUSTICAL STUDY OF THE PERCEPTION OF VOWEL-LIKE STIMULI

A two-formant synthetic vowel with closely spaced formants (F1 and F2 being fixed) can be made perceptually similar to a single-formant stimulus with F{black star} = (F1 + F2) 2 by adjusting the A2 A1-amplitude ratio of the formants. The critical distance between the formants (Δzc) that corresponds to the disappearance of this 'center of gravity' effect was found to be equal to 3.0-3.5 Bark. A close to continuous relation between A2 A1 and F{black star} of a single-formant matching stimulus was found for stimuli with Δz < Δzc. A clear discontinuous relationship between A2/A1 and F{black star} was observed for stimuli with Δz > Δzc. For stimuli with Δz > Δzc, the formant amplitudes appeared to be of minor importance, the vowel quality being determined by the frequency locations of the formant peaks in the vowel spectrum. Formant peaks can be detected even if they are represented by very small spectral irregularities. Possible relations between peak extraction and 'center of gravity' effects are discussed. © 1979.