The nonlinear relation between articulation and acoustics: Multiple constrictions
Khalil Iskarous · The Journal of the Acoustical Society of America · 2007
The vocal tract can be usefully approximated as a linear filter, but it has been known since the advent of this approximation that the relation between the area function and the acoustic output is nonlinear, despite linearity with respect to the input. This nonlinearity can be readily seen in nomograms displaying formants changing as a contriction changes its location or degree. It will be shown in this work that the nonlinear relation between area function and acoustics becomes even more significant when several constrictions are superimposed, which is the norm in natural speech production, where constrictions overlap in time. Simulations have been carried out, using a Kelly-Lochbaum digital lumped-loss transmission line, that show a complex relation between the formants resulting from a multiply constricted vocal tract to formants due to the constrictions when each is present by itself. The goal of the simulations is to predict time varying formant patterns when 2 or 3 constrictions are overlapped and all changing in time. A theory is then presented for how time-varying constrictions add in the acoustic domain. Implications for restrictions on compensation in speech production will be discussed. [Work supported by NIH NIDCD 02717.]