Phonatory stability refers to the steadiness and periodicity of vocal fold vibration, which is dependent on the laryngeal system maintaining relatively constant levels of muscular force during a sustained phonation (Ferrand 2006). The acoustic dimensions such as jitter, shimmer and harmonic-to-noise have been shown to reflect the stability of vocal fold vibration, referred to as phonatory stability. The current study was aimed at measuring phonatory stability in normal speaking children and adults. The Jitter, Shimmer and HNR values were obtained under auditorily masked and unmasked conditions. The details of the study are discussed in the chapters.