Two Voices
This additional source is another fascinating aspect of throat-singing. Singers draw on organs other than the vocal folds to generate a second raw sound, typically at what seems like an impossibly low pitch.
-“THE THROAT SINGERS OF TUVA on JSTOR,” 84.
While the vocal folds possess an impressive capacity to generate a wide array of sounds, it is actually the vocal tract that refines the raw sounds into both language and music. The vocal tract introduces a specific pattern to the combined sound produced by the folds, achieving this by selecting particular combinations of tones. These chosen tones align with the natural resonant frequencies of the air present within the vocal tract. When individuals speak or sing, they manipulate the resonant frequencies, also referred to as formant frequencies, by altering the positions of their tongue, lips, and other articulatory components.
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These movements are commonly perceived as alterations in vowel pronunciation. The initial formant frequency, F1, exhibits an inverse relationship with tongue elevation (F1 decreases as the tongue rises, such as the transition from /a/ in "hot" to /i/ in "heed"). On the other hand, the second formant frequency, F2, corresponds to tongue advancement (F2 increases as the tongue moves forward, similar to /o/ in "hoe" transitioning toward /i/ in "heed"). The vocal tract theoretically possesses an infinite number of formants, but the arrangement of the first two or three primarily accounts for the variations in vowel sounds.
Forming Formants
To comprehend the reasons behind shifts in formant frequencies, envision the vocal tract as a tube sealed at one end (the folds) and open at the opposite end (the lips). If the tube maintains a consistent cross-sectional shape, the resonant frequencies are dictated by the tube's length. For instance, a tube measuring 17.5 centimeters (approximately seven inches), comparable to the vocal tract of an adult male, results in F1 peaking at 500 hertz, F2 at 1,500 hertz, F3 at 2,500 hertz, and so forth. Each resonance signifies a stationary wave inside the tube. Consequently, air pressure oscillations (which transmit sound) and the corresponding molecular movement assume distinct patterns. Pressure nodes denote positions where pressure remains constant, while pressure antinodes signify points where pressure fluctuations are at their maximum, yet the molecules remain stationary. The closed end of the tube, restricted by the molecules' motion, acts as a pressure antinode, while the open end corresponds to a pressure node. As higher formants emerge, additional pairs of nodes and antinodes are introduced.
Now, envision the tube being constricted, mirroring the effect of the tongue narrowing the vocal tract. Although the alternating pattern of nodes and antinodes persists, the frequency shifts in proportion to the degree of constriction. A constriction near a pressure node results in a decrease in formant frequency, while a constriction near a pressure antinode leads to an increase. Conversely, expansion yields the opposite outcome. These principles were initially elucidated by Lord Rayleigh a century ago. At a node, constriction compels molecules to traverse a narrower opening, causing the wave's frequency to decrease as the air's motion requires more time. In contrast, at a pressure antinode, although the molecules remain stationary, their density fluctuates due to pressure variations that alternately draw them closer to and push them away from the antinode. As constriction reduces the tube's volume near the antinode, the introduction of a specific number of molecules generates a more significant density increase, resulting in greater pressure. Essentially, the system becomes stiffer and reacts more promptly, thereby elevating the wave frequency. A meticulous explanation, grounded in perturbation theory, delves into the altered shape that the stationary wave is compelled to adopt.
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Throat-singers routinely apply these principles in their practice. By pressing the base of the tongue against the back of the throat, where the second formant features a pressure node, they diminish the frequency of that particular formant. In the Tuvan sygyt style, practitioners elevate the middle of the tongue to constrict the antinode of the second formant, leading to an increase in its frequency.
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All technical images and the information provided here are sourced from Scientific American