Introduction

Vocal distortions have been studied since the 1970s, but debate continues regarding their terminology and the unclear physiological mechanisms behind them. Existing literature provides vague definitions or classifications, often based on the regions that produce the distortion, such as "Glottal" and "Supraglottal" distortions. This study, vocal distortions are defined as "sounds produced by the periodic and/or aperiodic vibration of glottic and/or supraglottic structures, potentially independent of the fundamental frequency." Key types of distortion include:

Rasp: A "sandpapery" sound from periodic/aperiodic ventricular fold vibrations.
Overcompressed Rasp: A more intense version of Rasp with strong adduction of ventricular folds.
Death Growls: A rough sound from aperiodic ventricular fold vibrations.
Metalcore Scream: An aggressive sound from multiple sources, often perceived as painful.
Grunts: A breathy, animalistic distortion with predominant breathiness.
These sounds are recognized in Catherine Sadolin's CVT methodology, potentially reducing terminological confusion. Most distortions originate from supraglottic structures, with the vocal folds typically acting as a tonal source.

Methods

The study used high-speed laryngoscopy and nasolaryngoscopy to analyze a trained metal vocalist (aged 25-30) performing Rasp, Overcompressed Rasp, Death Growls, Metalcore Scream, and Grunts.

Results

Rasp: Periodic vibrations of vocal folds were observed, with a V-shaped closure pattern in ventricular folds. Increased adduction of ventricular folds amplified distortion intensity.

Overcompressed Rasp: Stronger adduction of ventricular folds led to total closure, with a "collision" effect, heightening aperiodicity and aggressiveness.

Death Growls: Ventricular fold vibrations were aperiodic, and vocal folds were no longer medialized, eliminating recognizable tones.

Grunts: Distortion occurred solely at the vocal fold level, with a prolonged open phase, creating breathiness. Multiple vibratory periods produced a distorted effect.

Conclusion

Most vocal distortions involve supraglottic structures, particularly the ventricular folds. They can produce varied sounds, such as:

Rasp: Melodic due to periodic ventricular fold vibrations. Intensity is determined by adduction degree of the ventricular folds ,Ventricular folds vibrate in 1/2 of the f0 creating a "subarmonic"

Overcompressed Rasp: Distinguished from Rasp by noise-like quality due to collision of ventricular folds.

Death Growls: Noisier and more aperiodic than Rasp, with vocal fold abduction (less adducted) affecting tonal quality.

Grunts: A glottic sound with double periods; subglottic pressure and vocal fold adduction play key roles. Could be consider as a new vocal register/mechanism.