Nonlinear Source-Filter Coupling Due to the Addition of a Simplified Vocal Tract Model for Excised Larynx Experiments

Objectives Traditional excised larynx dissection and setup calls for the removal of all supraglottal structures, eliminating any source-filter interactions that measurably affect the acoustic properties of phonation. We introduce a simplified vocal tract model that can be used in the excised larynx experiments and tested the nonlinear source-filter interactions that are present with the addition of highly coupled, supraglottal structures. Methods Aerodynamic and acoustic data were measured at phonation threshold pressure (PTP) and +25% PTP in 10 excised canine larynges using a modified dissection technique. PTP and phonation threshold flow (PTF) were defined as the pressure and flow at the phonation onset; phonation threshold power (PTW) is the product of these values. Data were recorded for four experimental conditions: PTP without vocal tract; +25% PTP without vocal tract; PTP with vocal tract; and +25% PTP with vocal tract. Differences in PTP, PTF, and PTW were evaluated. For trials conducted at +25% PTP, differences in airflow were evaluated. Results PTP (Pآ =آ 0.009) and PTW (Pآ =آ 0.002) were significantly reduced with the addition of the novel vocal tract. A reduction in PTF was also present with the vocal tract (Pآ =آ 0.021), but airflow was not significantly reduced in +25% PTP trials (Pآ =آ 0.196). Conclusion The proposed vocal tract can be used with complete larynges when conducting excised larynx experiments. The effects of nonlinear source-filter interaction were observed during trials with the vocal tract, as evidenced by changes in threshold aerodynamic parameters.