Compare jitter, shimmer and harmonics to noise ratio in terms of the types of information each provides?
Jitter and shimmer are measures of the cycle-to-cycle variations of fundamental frequency and amplitude, respectively, which have been largely used for the description of pathological voice quality. Jitter is also known as frequency perturbation and refers to the minute involuntary variations in the timing variability between cycles of vibration. In essence, it is a measure of frequency variability in comparison to the client’s fundamental frequency. Research shows that jitter values in normal voices range from 0.2 to 1 percent. (Ferrand, 2007) Jitter values above this level indicate that the vocal folds are vibrating in a way that is not as periodic as it should be. (Ferrand, 2007). Higher jitter levels suggest that something is interfering with normal vocal fold vibration and the mucosal wave. (Ferrand, 2007)
Whereas jitter is a measure of the percentage irregularity in the pitch of the vocal note, shimmer is a measure of the percentage irregularity in the amplitude of the vocal note. It is often referred to as amplitude perturbation. Shimmer, therefore, measures the variability in the intensity of adjacent vibratory cycles of the vocal folds. Research estimates that shimmer values below 0.5 dB are normal in the human voice. (Ferrand, 2007). Jitter and shimmer reflect the internal noises of the human body. (Titze, 1994) As with jitter, pathological voices will typically exhibit a higher percentage of shimmer. Higher jitter and shimmer levels can reflect problems in neuromuscular control. 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. Measuring the cycle-to-cycle variability of vibration can allow us to detect changes in neuromuscular function or changes in the layers of the vocal folds. (Ferrand, 2007) The more steady...
References: Ferrand, C. T. (2007). In Speech science: An integrated approach to theory and clinical practice. Boston: Pearson/Allyn and Bacon.
Williamson, G. (2008, December 5). Instrumental Measurement of Voice. Speech Therapy: Information and Resources. Retrieved October 14, 2012, from http://www.speech-therapy-information-and-resources.com/instrumental-measurement-of-voice.html
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