This paper investigates vocal fold (VF) vibratory properties using quantitative analysis of high-speed digital imaging (HSDI) based on Nyquist-plot method derived from voicing during production of aberrant voice quality (VQ), clinically referred to as diplophonia, and defines the mechanism responsible for diplophonia and show how treatment (Tx) effects this VQ and VF behavior. In particular, pre- and post-Tx HSDI recordings of a female patient with muscular tension dysphoria (MTD) were analyzed using new quantitative analysis system for HSDI that involves tracing of VF edge and generation of glottal waveform and VF displacement, allowing us to define quantitative measures of vibratory symmetry and synchronization of VF vibrations, with subsequent analyses of glottal waveforms using Nyquist formula, to reveal vibratory pattern and characteristics of the vocal folds during this aberrant sound production, and later duiing normative phonation post Tx. This is first ever HSDI and Nyquist-plot based analyses of aberrant voice known as diplophonia derived here from vocalization of a MTD case. The results reveal definitive and specific character of VF vibration responsible for this VQ.

Index Terms. High-speed digital imaging, vocal-fold vibration, diplophonia, Nyqvist plot