Time-shift, trial, and gender effects on vocal perturbation measures

Three jitter and three shimmer measures were examined for: (1) the stability of the measured values with respect to shifts in sample site (starting point of window in the token) and (2) the effects of trial and gender. The perturbation measures and their coefficients of variation for windows starting from five different but adjacent cycles showed a dependence on sample size. Their variability with regard to shifts in sample site decreased asymptotically with increasing size. The data suggested no statistically significant trial effect except for APQ and no statistically significant gender effect except for absolute jitter. It is speculated that relatively long smoothing windows for shimmer (such as the one used for APQ) would allow the effects of slow vocal modulations (e.g., tremor) to accentuate, especially for lower pitch speakers.