Table 1.

A summary of the methods for estimating vocal tract resonances. Horizontal lines separate the three basic methods mentioned in the text. In this table, “ecological” refers to normal conditions of speech or singing, as distinct from special laboratory conditions.

	Excitation source	Measured parameters	Advantages	Disadvantages
	Vocal fold vibration (vocalization)	Sound output	• Natural source	• Unknown source spectrum
			• Ecological	• Poor frequency resolution
			• Minimal hardware	• Unusable at high pitch
			• No subject discomfort
			• Nonperturbing
	Turbulent air flow (whisper)	Sound output	• Natural source	• Unknown source spectrum
			• Minimal hardware	• Different mechanism causes  shift in formant frequencies
			• No subject discomfort
			• Non perturbing	• Not ecological
			• Good frequency resolution
	Mechanical excitation near glottis	Sound output and force input	• Can choose source spectrum • Good frequency resolution	• Perturbs subjects • Unknown transfer function   from skin to glottal flow • Not ecological • Requires hardware
	Acoustic current at lips	Tract and radiation impedance in parallel	• Can choose source spectrum • Good frequency resolution	• Measures “from wrong end” • Radiation impedance is low • Not ecological • Requires hardware
	None	Tract geometry inferred from tomography, acoustic properties calculated	• Gives explicit dependence   of acoustical properties   on articulation geometry	• Discomfort of subjects • Not ecological • Reduced frequency precision