|Lab: Objective Measurement of Breathy Voice
Breathy voice (also known as murmur) is one of the most common symptoms voice disorders, both organic and functional (Aronson, 1971; Aronson, 1990; Boone & McFarlane, 1988; Colton & Casper, 1990). There is also evidence that breathiness is associated with aging (Hollien, 1987; Ryan & Burk, 1974), and there is a tendency for women – on average - to produce somewhat breathier voices than men (Klatt & Klatt, 1990; McKay, 1987).
In terms of the underlying laryngeal vibratory pattern, two major features that are associated with breathy voice are described below.
Aspiration noise. The most obvious aerodynamic feature of breathy voice is that air escapes during the “closed” phase of the vibratory cycle. (The word closed is in quotation marks because, in the case of breathy voice, the vocal folds do not entirely meet at midline during the portion of the phonatory cycle in which glottal area reaches a minimum.) There is a surprising variety of laryngeal configurations that can be responsible for this air leakage, but the most commonly described (e.g., Södersten et al., 1995) is the posterior glottal (or glottic) chink, in which the anterior portion of the vocal folds periodically meet at (or near) midline (producing the buzzy component of breathy voice) while the posterior portion of the vocal folds remains open (producing the aperiodic, hissy component of breathy voice). This hissy component is called aspiration or aspiration noise. (This use of the term aspiration is entirely distinct from the use of this word in swallowing, referring to the entry of liquids or other unwanted gunk into the trachea and lungs.) Air leakage during the phonatory cycle results in turbulence, which is heard as noise.
The spectrum of aspiration noise – the hissy component of breathy voice – is stronger in the mid- and high-frequencies than it is in the lower frequencies. The spectrum of the buzzy (periodic) component of breathy voice, on the other hand, is exactly the opposite; i.e., it is stronger in the lower frequencies than it is in the highs. For this reason, aspiration is more easily seen in the mid-and high-frequencies, which the opposite is true of the periodic/harmonic component. These features can be seen in the spectra of Figure 2.
The presence of aspiration can be seen in the time domain: the waveform of a clearly phonated (modal) voice will appear highly periodic, and the degree of periodicity will decrease as the voice becomes more breathy. However, these differences in waveform periodicity are not always easy to see by eye – but they can usually be easily seen in the spectrum. For example, compare the narrow band spectra for the clear (non-breathy) and breathy voices in Figure 3. Notice that the degree of harmonic organization is much greater for the non-breathy voice; i.e., most of the energy is at harmonically related frequencies. The breathy voice, on the other hand, shows a reasonable degree of harmonic organization mainly in the low frequencies (see the glottal source spectra in the lower part of Figure 2). Differences in the degree of harmonic organization can also be seen in the output spectra (as opposed to source spectra) of Figure 3.