Acoustic, aerodynamic, physiologic, and perceptual properties of modal and vocal fry registers

The purpose of the study was to examine the acoustic, aerodynamic, physiologic, and perceptual characteristics of modal and vocal fry production. Twenty normal speakers (10 males, 10 females) participated in the study. Speech material included four sustained vowels (/i/, /a/, /ae/, /u/), and syllable strings of /pi/ repetitions produced in both modal and vocal fry registers. Acoustic data (fundamental frequency, jitter, shimmer, and signal-to-noise ratio), aerodynamic data (airflow and air pressure), and electroglottographic (EGG) data were obtained simultaneously. Results demonstrated considerable differences across voice parameters for the modal and vocal fry registers. Fundamental frequency was significantly lower in vocal fry than in modal register for both males and females, however, significant gender differences existed only in modal register. For both males and females, measurements of jitter and shimmer were significantly higher and signal to noise ratio was significantly lower in vocal fry. In addition, airflow rate in modal register was almost three times as high as the airflow rate in vocal fry register during sustained vowel production. During syllable string production, subglottal air pressure values in modal register were approximately 1.5 times higher than that in the vocal fry register. In general, these data emphasize that the aeromechanical mechanisms of vocal fold vibratory behavior are substantially different between modal and vocal fry registers. A model of vocal fry phonation is presented to account for the present results.