Table 4.

Vocal variables with x   ∈ [a, e, i, o, u].

Vocal variable	Description
xF0	Average fundamental frequency
xJITT	Jitter (cycle-to-cycle variation of fundamental frequency)
xRAP, xPPQ	Relative average perturbation and pitch perturbation quotient (frequency variation characteristics)
xSHIM	Shimmer (cycle-to-cycle variation of amplitude)
xAPQ	Amplitude perturbation quotient
xF1, xF2, and xF3	1st, 2nd, and 3rd formant frequencies
xBW1, xBW2	Bandwidths of the 1st and 2nd formants
sDT	Duration of sentence utterance
sF10, sF50, and sF90	Fundamental frequencies at the 10th, 50th, and 90th percentiles (sentence)
sFHL	Ratio of the frequency intervals between a high to the median and the median to a low fundamental frequency = (sF90 − sF50)/ (sF50 − sF10)