Jitter and Shimmer

Acoustic measures of voice quality that capture short-term irregularity in the vocal fold vibration. Jitter is the cycle-to-cycle variability in pitch (fundamental frequency), while shimmer is the cycle-to-cycle variability in amplitude. Elevated jitter and shimmer are associated with hoarseness, breathiness, and vocal pathology, and have been documented in aging, Parkinson's disease, dysarthria, and cognitive impairment including Alzheimer's disease and related dementias. These features are relevant to accessibility because they correlate with reduced automatic speech recognition accuracy and can motivate speaker-personalized or voice-quality-aware ASR adaptation.