Analysis and Categorization of Various Types of Vocal Distortion in Rock, Metal, Pop Styles, and Throat Singing Observed by High-Speed Digital Imaging.

Introduction: Vocal distortion, also known as a scream or growl, is used worldwide as an essential technique in singing, especially in rock and metal, and as an ethnic voice in Mongolian singing. However, the production mechanism of vocal distortion is not yet clearly understood owing to limited research on the behavior of the larynx, which is the source of the distorted voice.

Objectives: This study used high-speed digital imaging (HSDI) to observe the larynx of professional singers with exceptional singing skills and determine the laryngeal dynamics in the voice production of various vocal distortions. In addition, this study aimed to classify vocal distortions based on laryngeal dynamics.

Study design: Cross-sectional study.

Methods: The dynamic behavior of the larynx of six singers (four males and two females) was recorded using HSDI, with the majority of recordings captured at frame rates exceeding 8000 fps. The audio signals were recorded simultaneously. The data were analyzed as topography, glottal area waveforms, long-term average spectra, and spectrograms.

Results: Our analysis revealed that, based on the laryngeal vibration pattern, vocal distortion could be categorized into two primary groups: "periodic" and "aperiodic." In the "periodic" distorted vocalizations, it was suggested that the glottal sound source containing overtone components is generated by vocal fold vibrations, and subharmonic components in the voice are the result of amplitude modulation of the glottal jet by vibrations in the supraglottic region. However, "aperiodic" distorted vocalizations were found to be generated by the vocal folds, which are the main source of noise and generate strong noise due to aperiodic chaotic oscillations of the vocal folds.

Conclusion: The diversity of distorted vocalizations is due to the physiologically and acoustically complex mechanism of voice production in the larynx.