ACOUSTIC INTERACTIONS OF THE VOICE SOURCE WITH THE LOWER VOCAL-TRACT

The linear source-filter theory of speech production assumes that voca l fold vibration is independent of the vocal tract. The justification is that the glottis often behaves as a high-impedance (constant flow) source. Recent imaging of the vocal tract has demonstrated, however, t hat the epilarynx tube is quite narrow, making the input impedance to the vocal tract comparable to the glottal impedance. Strong interactio ns can exist, therefore. In particular, the inertance of the vocal tra ct facilitates vocal fold vibration by lowering the oscillation thresh old pressure. This has a significant impact on singing. Not only does the epilarynx tube produce the desirable singer's formant (vocal ring) , but it acts like the mouthpiece of a trumpet to shape the flow and i nfluence the mode of vibration. Effects of the piriform sinuses, phary nx expansion, and nasal coupling are also discussed. (C) 1997 Acoustic al Society of America.