An algorithm for the measurement of jitter

Abstract Jitter is the small fluctuation from one glottis cycle to the next in the duration of the fundamental period of the voice source. Analyzing jitter requires measuring glottal cycle durations accurately. Generally speaking, this is carried out by sampling at a medium rate and interpolating the discretized signal to obtain the required time resolution. In this article we describe an algorithm which solves the following two signal processing problems. Firstly, signal samples obtained by interpolation are only estimates of the original samples, which are unknown. The quality of the reconstruction of the signal therefore has to be evaluated. Secondly, small variations in cycle durations are easily corrupted by noise and measurement errors. The magnitude of measurement errors therefore has to be gauged. In our algorithm, the quality of reconstruction by signal interpolation is evaluated by a statistical test which takes into account the distribution of the corrections (which are brought about by interpolation) to the positions of the signal events which mark the beginnings of the glottal cycles. Three different interpolation methods have been implemented. Measurement errors are controlled by estimating independently the cycle durations of the speech and the electroglottographic signals. When the series obtained from both signals agree, we may then conclude that they reflect vocal fold activity and that they have not been unduly corrupted by errors or noise. The algorithm has been tested on 77 signals produced by healthy and dysphonic subjects. Its performance was satisfactory on all counts.