Vocal tract acoustics reduce to a cross-sectional area function along one axis

Evidence

The vocal tract acts as an acoustic transmission line where the glottal excitation propagates to the lips. While the uvular link to the nasal cavity is open, the coupling of the nasal tract creates nasal or nasalized sounds. The shape of the tract is determined by the position of the tongue and its tip, the opening of the jaw, and the shape of the lip opening. From an acoustic point of view, the transmission properties of the vocal tract are due to the cross-sectional area function of the tract A(x), where x is the position in the glottis–lips dimension. According to Equation (2.23), the acoustic impedance at each point is Za(x) = ρc/A(x); that is, it is inversely proportional to the area. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 613

Categorization

• DEFINE: Clarifies the transmission-line framing of the vocal tract central to source-filter speech models.