Hoarseness technically is an impairment of the signal-to-noise ratio of the human voice, although perhaps a descriptive definition might be more helpful. Hoarseness is unintentional non-harmonic passage of air between vibrating vocal cords. That is, the unwanted leak of air though the vocal cords or the irregular passage of air through the vocal cords.
Air leak and diplophonia
All hoarseness can be described in these two ways. In the first, the vocal cords do not come together as they should, allowing air leak. Let’s call this husky hoarseness. This is white noise. The second type of hoarseness is caused by asymmetric vibration. Because there are two vocal cords, when they are not symmetric, they tend to vibrate at two different pitches. A physician would call this sound diplophonia. Di- meaning "two" and -phonia meaning "voice", so two voices can be heard at once. Usually, since the vocal cords are only slightly out of sync, the diplophonia will be inharmonious and the perception will be of a rough or gravelly quality. We will call this rough hoarseness.
Simply put, there are only two ways to be hoarse.
- Air is leaking when you don’t want it to leak. This is called husky hoarseness.
- The vocal cords are vibrating irregularly. This is called rough hoarseness.
While “white noise” is considered a technical term and “breathiness” could be considered a non-technical term, breathiness has clearly been used in voice literature for at least 5 decades. White noise has a flat spectrum over the audible frequency range and is perceived as a /sh/ sound. Because breathinessis such a common term in laryngology literature, we will consider white noise and breathiness as synonyms.
Nearly the same can be said of the term “roughness”. Roughness is a consumer-type term that has been used in laryngology literature for decades. It represents the perceived quality of two or more tones, which are not multiples of each other. When two non-harmonic tones interact, the sound waves cancel and multiply with each other in terms of volume, altering our perception of the sound. Voice loses clarity. We often hear the term diplophonia when there are two almost distinct tones, but depending on the spectral distance from each other, it may be difficult to perceive whether there are two tones or several tones. We could hear a triplophonic sound, or more generally stated, a polyphonic sound. In day-to-day musical terms though, polyphony is perceived as beautiful, as when an orchestra is in tune and more than one note harmonically blends with related notes. For this website though, the terms roughness, diplophonia and polyphonia are effectively used as synonyms.
Summary
There are only two ways to be hoarse.
- Air is leaking when you don’t want it to leak. This is called husky hoarseness.
- The vocal cords are vibrating irregularly. This is called rough hoarseness.