Inter- and intrasubject changes in vibrato: Perceptual and acoustic aspects

Recent papers by Rothman and Timberlake (1), Rothman (2), Rothman and Arroyo (3), and Keidar, Titze, and Timberlake (4) have focused on the pulse rate, frequency extent, and amplitude extent of vibrato. Some of the emphases of these papers were attempts to clarify the acoustic and perceptual correlates of vibrato, tremolo, and wobble. Rothman and Arroyo (3) speculated that the shape of the frequency variation waveform may be indicative of vocal problems. In order to verify this, we examined recorded segments of sung samples produced by different singers and samples taken from the early and late stages of singers' careers. Some singers had a relatively short career before exhibiting vocal problems. Others had relatively long careers before showing evidence of vocal decline. Many, but not all, of the singers' late career recordings represent examples generally acknowledged to evidence vocal problems/decline. Each sample was digitized at a sampling frequency of 10 kHz, stored, and analyzed using programs reported on by Rothman and Arroyo (3). Data analysis revealed that some parameters can distinguish between good and bad vibrato despite the variance in listener judgments. Furthermore, evidence of vocal decline is not always due to changes in singers' vibrato.