On the harmonic-to-noise ratio as an acoustic cue of vocal timbre of Parkinson speakers

The relevance of the harmonic-to-noise ratio (HNR) and glottal cycle length jitter as cues of the vocal timbre of Parkinson speakers is investigated. HNR and vocal cycle length jitter are known to be suitable cues for the evaluation of the vocal timbre of dysphonic speakers. However, the question whether they are relevant descriptors of the voice quality of Parkinson speakers is still unanswered. Empirical mode decomposition (EMD) has been used to estimate the HNR by decomposing the log-magnitude spectrum of the speech signal into its harmonic, contour and noise components. Cycle length jitter has been estimated via the break-up by empirical mode decomposition of the cycle length time series into the intonation contour as well as the perturbations owing to tremor and jitter. HNR and cycle length jitter values of vowels [a] sustained by 205 Parkinson and 74 control speakers are in the same interval respectively and the differences are not statistically significant. Also, the standard deviations of the per-frame HNR values of an utterance do not differ statistically significantly between control and Parkinson speakers.