Ferrand, The more steady the muscles that control vocal fold vibration are, the more steady and periodic the acoustic signal will be and the lower the jitter and shimmer.
Titze, As with jitter, pathological voices will typically exhibit a higher percentage of shimmer. Speech Therapy: Information and Resources.
Jitter is also known as frequency perturbation and refers to the minute involuntary variations in the timing variability between cycles of vibration. The aperiodic waves are random noise introduced into the vocal signal owing to irregular or asymmetric adduction closing of the vocal folds.
Ferrand, Increased levels of jitter and shimmer can also be caused by a nodule or cyst on the vocal folds which would increase the vocal fold mass and vibration would become less periodic.
Noise impairs the clarity of the vocal note and too much noise is perceived as hoarseness. Popular Essays. Laryngeal pathology may lead to poor adduction of the vocal folds and, therefore, increase the amount of random noise in the vocal note.