Air leak white noise

To understand husky hoarseness, it is helpful to think of one of the extreme types of sound production we can make with our larynx normally: extremely soft sound. We can generate sound in the larynx with the vocal cords in a partially or completely open position – that sound is called a whisper. 

During normal sound production, the membranous vocal cords lie parallel to each other and vibrate – opening and closing. Although the posterior aspect of the vocal cords are hidden from view beneath the arytenoids in the photo, the back of the membranous vocal cords are together. This stroboscopic photo was taken during the closed phase of vibration, when the central portion of the vocal cords are closest together.

By contrast, in a whisper, the vocal cords do not vibrate. The airflow is increased and as it passes a narrowed spot, turbulence is created. Airflow that is turbulent consists of many different pitches simultaneously: white noise. The larynx can narrow the airway in several ways without allowing the vocal cords to vibrate. 

In a true whisper, the back of the larynx might be open between the vocal processes while the membranous vocal cords might be closed such that all the air is forced out through this triangular opening at the posterior end of the membranous true vocal cords.

The signal generated by airflow through this triangle, consisting of white noise, lacks intensity and cannot be heard well or from very far away. It is not very penetrating. It has a low signal-to-noise ratio. White noise blends with environmental noise. For example, open the car windows while traveling and a great deal of turbulent airflow is created at the window. This white noise effectively masks other sounds. A whisper, which is also white noise, in a car blends in with the sound created by the open windows and cannot be heard at all.

Conversely, we typically produce voice at a single pitch to generate a strong signal that will stand out against background noise. This is a signal that we modify with vowels and consonants to carry information from one human to the next. With a clear tone we can generate sounds that are distinct and carry well, even in a convertible on the highway driving with the top down.

A stage whisper is meant to sound like a whisper, yet the audience needs to hear the speaker. In a stage whisper for a theatre production, the vocal cords are allowed to vibrate a little, so that the sound has the character of white noise, but enough vibrations of the vocal cords for the sound to carry into the audience. A stage whisper is really a mixture of air turbulence and some vibration.

In between a whisper (cords not vibrating, very low signal to noise ratio) and a clear tone (cords completely parallel with all air passing between them, very high signal to noise ratio), we can have some mix of a pure tone and white noise. The white noise gives the voice a husky quality.

Later in this book, we will examine individuals where this huskiness is not desired and air is leaking out unintentionally. Other times, for example, a nightclub singer might wish to add a component of breathiness to her voice to give it a sexy quality. She is adding an intentional gap between the vocal cords to let some air leak out. A novice singer may be straining so hard, she ends up tensing multiple muscles in the larynx and inadvertently holds the vocal cords apart.

So while a whisper is the extreme of turbulent airflow through the larynx, any gap between the vocal cords will add a commensurate degree of turbulence perceived as a huskiness of the voice. We may desire that quality, but if we don’t, it is hoarseness.