Jitter and Shimmer in Sustained Phonation

Publisher Summary This chapter discusses one specific aspect of vocal fold vibration, namely, its periodicity in sustained phonation. Presence of small perturbation or irregularity of glottal vibration in normal voice has long been known through oscillographic analysis of acoustic pressure waves and through laryngoscopy high-speed photographic investigations. Variations of fundamental frequency (period) and amplitude of successive glottal pulses, in particular, are often referred to as jitter and shimmer, respectively. Because of their minute nature, their measurements were time consuming and difficult, and normative data on jitter and shimmer have been slow to accumulate. However, recently some methods of measurements, normative data and data from pathologic larynges, perceptual studies of jitter and shimmer, and neurophysiological interpretations of jitter and shimmer have provided new insight. Attempts have been initiated in formulating mechanical and neuromuscular models of normal and pathologic vocal perturbation