Predictable and random components of jitter

The subject of this article is the study of the deterministic and random components of jitter by means of a statistical time series model. Jitter is the small fluctuations in glottal cycle lengths. The purpose of time series analysis is to take into account the fact that glottal cycles are produced sequentially and that relations between neighbouring perturbations exist. The jitter time series model statistically represents the present perturbation as a weighted sum of past perturbations and random noise. The model is fitted to observed jitter time series by means of conventional linear methods. A discriminant analysis of jitter time series extracted from 279 sustained vocoids [a] [i] [u] shows that the jitter features which separately describe the predictable and random components better characterise healthy and dysphonic speakers than a traditional jitter feature. The conclusion is that the relations between neighbouring cycle length perturbations are an aspect of jitter independent of the scatter of the cycle lengths which is described by conventional jitter features.