Source-vocal tract interaction in singing
Ingo R. Titze · The Journal of the Acoustical Society of America · 2007
It has been known for centuries that certain vowels are easier to sing on certain pitches. Much of traditional and modern singing pedagogy is focused on this vowel F0 interaction. Unlike most musical instruments, where the resonator is specifically designed to resonate many of the source frequencies at every note played, the vocal instrument relies on the use of inertive reactance (away from resonance) to boost various clusters of harmonics. Acoustic reactance is positive (inertive) below a vocal tract resonance (a formant), zero at resonance, and negative (compliant) above resonance. The skill in selecting a vowel for a given F0 is to place as many of the key harmonics (2F0, 3F0, and 4F0) on the inertive portions of the reactance curves. The process is aided by shrinking the epilarynx tube, which biases the reactance curves toward positive values over the entire F0 range. [Work supported by NIDCD.]