Source characteristics of diplophonia
Bruce R. Gerratt, Kristin Precoda, David G. Hanson, Gerald S. Berke · The Journal of the Acoustical Society of America · 1988
Diplophonia describes the perception of more than one fundamental frequency component in a voice. Simultaneous photoglottographic (PGG), electroglottographic (EGG), and acoustic signals were collected from five diplophonic subjects. Results indicate that diplophonia is similar to the beat frequency phenomenon caused by independent vibration of the two vocal folds at slightly different frequencies. In the time domain, modeling vocal fold displacement from midline by summing two sine waves produced area waveforms closely resembling the PGG waveforms obtained from the diplophonic subjects. In the frequency domain, the diplophonic voice spectrum bears little resemblance to that of normal phonation. Instead of the normal set of harmonic peaks at integer multiples of the fundamental, the diplophonic spectrum shows a wealth of very closely spaced energy peaks of which the two fundamentals are often the most prominent but rarely the lowest frequency. The spectral envelope of the glottal area waveform may appear to have poles where no formants are possible and the spectral energy falls off quite rapidly. The locations of prominent energy peaks were predicted by modeling the displacement of the vocal folds from midline using the sum of two sine waves clipped by pulse trains to simulate collision effects of the two vocal folds. [Work supported by NINCDS.]