Source and filter adjustments affecting the perception of the vocal qualities twang and yawn

Two vocal qualities, twang and yawn, were synthesized and rated perceptually. The stimuli consisted of synthesized vocal productions of a sentence-length utterance 'ya ya ya ya ya,' which had speech-like intonation, In a continuum transformation from normal to twang, the area in the pharynx was gradually decreased, along with vocal tract shortening and a decreased open quotient in the glottal airflow. In a continuum transformation toward yawn, the area in the pharynx was gradually increased, along with vocal tract lengthening and an increased open quotient. The normal (untransformed) vocal tract area was pre-determined by earlier studies involving MRI scans of a human subject's vocal tract. Listeners were asked to rate (on a scale from 1-10) the 'amount of twang' in one listening session and the 'amount of yawn' in another listening session. Overall, the perception of twang increased directly with pharyngeal area narrowing, vocal tract shortening, and decreased open quotient. The perception of yawn increased with pharyngeal area widening, vocal tract lengthening, and increased open quotient. Adjustments of one parameter alone yielded less significant perceptual changes than the above combinations, with open quotient showing the greatest effect in isolation. Listeners demonstrated variable perceptions in both continua with poor inter-subject, intra-subject, and inter-group reliability.