Supraglottic Distortion

Abstract

Distortion is an aperiodic effect that introduces especially loud ‘noise’ to the voice. Supraglottic distortion is a classification of distortion originating from vibratory activity above the level of the vocal folds.

Definition and classification

Periodic sounds in a strict sense are sounds that repeat exactly over and over again. In reality, the human voice is not a perfect machine so normal vocal fold vibration tends to actually be ‘quasi-periodic’ (i.e., almost periodic; they repeat in a noticeably similar way over and over). This too is scientifically considered a periodic sound.

Aperiodicities are, therefore, sounds that do not repeat. They’re effectively noise. However, this doesn’t mean that a periodic supraglottic vibration doesn’t count as an aperiodicity. If that vibratory behavior is out of sync with the vocal fold motion, that is also considered an aperiodicity. So, in general, aperiodicities are sounds that are out of sync with vocal fold motion.

Distortion occurs when the aperiodic noise picks up enough intensity to significantly compete with the periodic sound output originating from the vocal folds.

Growl is a type of distortion. Like most things in voice, because it’s a colloquial term, its definition is highly variable in different communities. However, the approximate definition is that it’s a heavier distortion with supraglottic vibration (vibration of bodies above the vocal folds) that tends to be lower in pitch than what people would call scream and/or less ringy.

In addition to growl, there are several other forms of more specifically used terms to define supraglottic distortions in the voice.

Anatomy of supraglottic distortions

The supraglottic vibrations involve three accessory vibrating bodies that are positioned above the vocal fold level. These are the epiglottis, aryepiglottic folds, and ventricular folds (which are also known as false vocal folds):

A top-down view of the larynx.

The epiglottis is the highest of these vibrating bodies. It’s shaped like a leaf hanging back from the root of the tongue over the larynx (the voice box). When the tongue rises during swallowing, the epiglottis goes down to cover the opening to the larynx, preventing food and liquid from entering the larynx and, consequently, the trachea and lungs.

To locate and feel the epiglottis, one can produce a sound known as knödel. This borrowed German word describes the sound of phonating with a dumpling in your mouth. During knödel, the back of the tongue pushes the epiglottis back so it folds over the larynx. In this position, it is predisposed to vibrate with sufficient air pressure.

The aryepiglottic folds extend all the way from the sides of the epiglottis down to the arytenoid cartilages, where the vocal folds attach. Their constriction approximates the epiglottis and arytenoid cartilages, highlighting piercing frequencies above the note we perceive. It’s this characteristic that allows babies’ voices to carry over loud ambient noise with high spectral energies that instinctively trigger human attention.

A witch voice can act as a trigger to locate and feel the aryepiglottic folds constrict. From a controlled position of constriction, the aryepiglottic folds can be triggered to vibrate with sufficient air pressure.

The false vocal folds (FVFs; also called vestibular folds or ventricular folds) sit right above the true vocal folds. Like the epiglottis, they help prevent food aspiration.

Making a wheezing sound can act as a trigger for extending the false vocal folds. While extended, sufficient air pressure can move the false vocal folds to vibrate.

In paradoxical vocal fold motion disorder (PVFMD), both the true vocal folds and the false vocal folds constrict during inhalation and relax during exhalation. This paradoxical breathing behavior causes difficulty in breathing accompanied by a wheezing sound. Symptoms are usually confused with those of asthma.

Sustainability

Supraglottic distortion involves a contraction that allows the vibration of the body in question to be motivated by airflow. The vocal folds shouldn’t come closer to each other in order to reach the threshold pressure for supraglottic vibration — their contraction should be minimized.

With that in mind, supraglottic distortion has been proven to be safe in both the short and long-term.

Growl

The definitions vary from source to source. A definition is proposed here in “Anatomy of a growl”.

Squall

TVF: Mid to high M1/M2

FVF: more aggressively vibrated

Aryepiglottic folds: vibration and twang are common

Roar

TVF: Lower pitched M1/M2 (usually M1)

FVF: variable vibration levels

Low larynx position

Rumble

TVF: Variable

Epiglottis: Vibrated

Scream

TVF: High pitch M2/M3

FVF: Aggressively vibrated

Subharmonics

TVF: Low pitched M1

FVF: Aggressively vibrated at a frequency about half the TVF vibration

Aryepiglottic folds: Variable

Conclusion

The dynamic combinatory engagement of the true vocal folds and different supraglottic vibratory bodies creates a vast array of types of supraglottic distortion.

Whether the aryepiglottic folds participate in supraglottic distortion is still under scientific review.

References

Aaen, M., Mcglashan, J., & Sadolin, C. (2020). Laryngostroboscopic Exploration of Rough Vocal Effects in Singing and their Statistical Recognizability: An Anatomical and Physiological Description and Visual Recognizability Study of Distortion, Growl, Rattle, and Grunt using laryngostroboscopic Imaging and Panel Assessment. Journal of Voice34(1). doi: 10.1016/j.jvoice.2017.12.020

Caffier, P. P., Nasr, A. I., Rendon, M. D. M. R., Wienhausen, S., Forbes, E., Seidner, W., & Nawka, T. (2018). Common Vocal Effects and Partial Glottal Vibration in Professional Nonclassical Singers. Journal of Voice32(3), 340–346. doi: 10.1016/j.jvoice.2017.06.009

Paradoxical Vocal Fold Motion Disorder. Retrieved from http://www.otolaryngology.pitt.edu/centers-excellence/voice-center/conditions-we-treat/paradoxical-vocal-fold-motion-disorder

http://www.cas.usf.edu/~frisch/SPA3011_L06.html