How are two tones produced simultaneously in throat-singing?

Abstract

The most remarkable characteristic of throat-singing is that one singer simultaneously produces two distinct tones—drone and melody. The drone has a low and sustained pitch, and is sung with a pressed voice. The melody has a whistlelike tone, whose pitches are much higher than the drone. It was conjectured that the production of the melody was caused by the resonance of the vocal tract, but has never been proved. This study clarifies that the high melody pitch is produced by the pipe resonance of the rear cavity in the vocal tract. This is derived from acoustic investigations on a throat-singer’s vocal tract measured by magnetic resonance imaging. Four different shapes of the vocal tract are examined, with which the melody pitches of F6, G6, A6, and C7 are sung along with the F3 drone of a specific pressed voice. The second formant frequency calculated from each tract shape is close to the melody pitch within an error of 36 cents. Sounds are synthesized by convolving a glottal source waveform with transfer functions calculated from the vocal tract shapes. Two pitches are found to be successfully perceived when the synthesized sounds are listened to.