Frequency response of the vocal tract considering the glottis opening area during human whistling

What is it about?

The principles of whistling in relation to pronunciation are reported to be based on Helmholtz resonance. However, some whistlers can produce high-register sounds by blowing harder without changing the capacity of the resonance chamber, similar to how a high-register sound can be produced in a wind instrument via air column resonance; thus, our research group configured a vocal tract model using computed tomography (CT) data acquired during whistling performance, and showed that fundamental frequency changes due to overblowing, and that this frequency corresponds to resonance frequency of the vocal tract. However, there was a problem: namely, some sounds with pitch corresponding to calculated resonance frequencies did not occur. In the present study, the glottis opening area during whistling was measured via endoscopic imaging data. The amplitude characteristics of the vocal tract were determined by measuring the glottis opening area during whistling and calculating the transfer function of the vocal tract in conjunction with that area. By considering the glottis opening area, we could logically explain the fact that, in reality, some notes corresponding to theoretically calculated resonance frequencies did not occur, and we could obtain a calculation result that was close to the physical model. Furthermore, because the calculation result close to the physical model was only associated with certain glottis opening areas, it is evident that not only the shape of the vocal tract and the lip opening area, but also the glottis opening area is an important component of sound production during human whistling.

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Photo by Marco Perretta on Unsplash

Photo by Marco Perretta on Unsplash

Why is it important?

Whistling has become more popular in recent years. However, not everyone can whistle, and it can be difficult to teach some people how to whistle. One of the reasons is that theoretical information, including clear descriptions about how to whistle is scant. A better understanding of the principle would be beneficial to both the trainer and the trainee. Not only vocal tract shape and lip opening area, but also glottis opening area is an important factor, while decline in gain with dilated glottis indicates that the glottis opening is related to whistling sound volume.