中科大语音信号处理课件ch5.pdf

Chapter 5 Sound Propagation in the Human Vocal Tract 声道中的声音传播 1 Basics • can use basic physics to formulate air flow equations for vocal tract • need to make simplifying assumptions about vocal tract shape and energy losses to solve air flow equations 2 Sound in the Vocal Tract • Issues in creating a detailed physical model – time variation of the vocal tract shape (we will look mainly at fixed shapes) – Losses due to heat conduction and friction in the walls (we will first assume no loss, then a simple model of loss) – softness of vocal tract walls (leads to sound absorption issues) – radiation of sound at lips (need to model how radiation occurs) – nasal coupling (complicates the tube models as it leads to multi-tube solutions) – excitation of sound in the vocal tract (need to worry about vocal source coupling to vocal tract as well as source-system interactions) 3 Vocal Tract Transfer Function 4 Schematic Vocal Tract PDEs must be solved in this region • simplified vocal tract area = non-uniform tube with time varying cross section • plane wave propagation along the axis of the tube (this assumption valid for frequencies below about 4000 Hz) • no losses at walls