Spectral analysis of digital kymography in normal adult vocal fold vibration

The purpose of this study was to examine the spectrum of normal adult vocal fold vibration obtained through direct visualization technique using digital kymography (DKG). DKG extracts high-speed kymographic images of each vocal fold sampled at a single or multiple points along the vocal folds. Thus, direct and objective quantification of the cycle-to-cycle movements of the left and right vocal folds were obtained. In this study, DKG spectrum configuration in males and females were examined. Samples were obtained from seven subjects (three males and four females) with no history of voice disorders. Subjects were asked to produce tokens obtained from a standard clinical laryngeal evaluation producing tokens at modal, low, and high frequency and at modal frequency with increased loudness. Results demonstrated that the spectrum of normal adult phonation consisted of a large and robust H1 (fundamental frequency) and significant attenuation of power in the higher harmonics (H2, H3). The spectral peaks were quasiperiodic with no spectral smearing. Analysis of the spectral data revealed variations in the spectrum that were influenced by the frequency of phonation and gender. Subjects demonstrated a range of left-right asymmetry of the spectral peaks (2-26%). This study presents a preliminary database of direct spectral characteristics of normal adult vocal fold vibration over a range of frequencies and intensities. Furthermore, these measures provide data from which similar measures obtained from dysphonic pathologies can be compared.