Low-frequency vocal modulations in vowels produced by Parkinsonian subjects

Low-frequency vocal modulations here designate slow disturbances of the phonatory frequency F0. They are present in all voiced speech sounds, but their properties may be affected by neurological disease. An analysis method, based on continuous wavelet transforms, is proposed to extract the phonatory frequency trace and low-frequency vocal modulation in sustained speech sounds. The method is used to analyze a corpus of vowels uttered by male and female speakers, some of whom are healthy and some of whom suffer from Parkinson’s disease. The latter present general speech problems but their voice is not perceived as tremulous. The objective is to discover differences between speaker groups in F0 low-frequency modulations. Results show that Parkinson’s disease has different effects on the voice of male and female speakers. The average phonatory frequency is significantly higher for male Parkinsonian speakers. The modulation amplitude is significantly higher for female Parkinsonian speakers. The modulation frequency is significantly higher and the ratio between the modulation energies in the frequency bands [3 Hz, 7 Hz] and [7 Hz, 15 Hz] is significantly lower for Parkinsonian speakers of both genders.