Acoustic Tube Modeling (I) 虞台文
Content Introduction Wave Equations for Lossless Tube Uniform Lossless Tube Lips-Radiation Model Glottis Model One-Tube Vocal Tract Model Exercises
Acoustic Tube Modeling (I) Introduction
Vocal Tract
Acoustic Tube Derivation Lips Glottis
Assumptions Lips Glottis Consists of M interconnected sections of equal length, and each section is of uniform area. The traverse dimension of each section is small enough compared with a wave length so that the sound propagation though an individual section can be treated as a plane wave. Sections are rigid so that internal losses due to wall vibration, viscosity, and heat conduction are negligible. The model is linear and uncoupled from glottis. The effects of the nasal tract can be ignored.
Discrete Area Functions Lips Glottis Area Lips Glottis
Acoustic Tube Modeling (I) Wave Equations for Lossless Tube
dx ( 密度 ) V ( 體積 ) A ( 面積 ) A+dA 壓力 (p) 壓力 (p+dp) m= V ( 質量 ) F v ( 速度 ) u ( 容積速度 ) Eliminate higher order terms
Wave Equations for Lossless Tube dx ( 密度 ) V ( 體積 ) A ( 面積 ) A+dA v ( 速度 ) u ( 容積速度 ) p ( 壓力 ) v+dv u+du Mass Continuity Condition
Wave Equations for Lossless Tube dx ( 密度 ) V ( 體積 ) A ( 面積 ) v ( 速度 ) u ( 容積速度 ) p ( 壓力 ) v+dv u+du Mass Continuity Condition
Vocal Tract A(x, t) x=0x=lx=l GlottisLips u(x,t)u(x,t) p(x,t)p(x,t)
Acoustic Tube Modeling (I) Uniform Lossless Tube
Uniformly Lossless Tube x=0x=lx=l
Uniformly Lossless Tube x=0x=lx=l
Uniformly Lossless Tube x=0x=lx=l
Pressure vs. Volume Flow x=0x=lx=l u(x,t)u(x,t) u+(tx/c)u+(tx/c) u (t+x/c)u (t+x/c)
Pressure vs. Volume Flow
0 Characteristic Impedance of the tube.
x=0x=lx=l u+(t)u+(t) u+(tl/c)u+(tl/c) u(t)u(t) u(t+l/c)u(t+l/c) u+(tx/c)u+(tx/c) u(t+x/c)u(t+x/c) + u(x,t)u(x,t) + + Z p(x,t)p(x,t) Pressure vs. Volume Flow
x=0x=lx=l u+(t)u+(t) u+(tl/c)u+(tl/c) u(t)u(t) u(t+l/c)u(t+l/c) u+(tx/c)u+(tx/c) u(t+x/c)u(t+x/c) + u(x,t)u(x,t) + + Z p(x,t)p(x,t) Pressure vs. Volume Flow 壓力受順流與逆流 強度和而改變
Acoustic Tube Modeling (I) Lips-Radiation Model
Boundary Condition (Lips) Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips ZLZL ZLZL p L (t)=p T (l, t) u L (t)=u T (l, t) Radiation Impedance Assumed Z L (j ) is real
Boundary Condition (Lips) Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips ZLZL ZLZL p L (t)=p T (l, t) u L (t)=u T (l, t) Assumed Z L (j ) is real
Boundary Condition (Lips) Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips ZLZL ZLZL p L (t)=p T (l, t) u L (t)=u T (l, t)
Boundary Condition (Lips) Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips ZLZL ZLZL p L (t)=p T (l, t) u L (t)=u T (l, t)
Boundary Condition (Lips) Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips ZLZL ZLZL p L (t)=p T (l, t) u L (t)=u T (l, t) 1+ L Delay LL In case Z L 0, L = 1 In case Z L 0, L = 1
Acoustic Tube Modeling (I) Glottis Model
Boundary Condition (Glottis) uG(t)uG(t) ZGZG ZGZG Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips
Boundary Condition (Glottis) uG(t)uG(t) ZGZG ZGZG Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips p G (t)=p T (0, t) Assumed Z G (j ) is real
Boundary Condition (Glottis) uG(t)uG(t) ZGZG ZGZG Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips p G (t)=p T (0, t) Assumed Z G (j ) is real
Boundary Condition (Glottis) uG(t)uG(t) ZGZG ZGZG Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips p G (t)=p T (0, t) Assumed Z G (j ) is real
Boundary Condition (Glottis) uG(t)uG(t) ZGZG ZGZG Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips In case Z G >> 0, G =1 In case Z G >> 0, G =1 Delay
Acoustic Tube Modeling (I) One-Tube Vocal Tract Model
One-Tube Model uG(t)uG(t) ZGZG ZGZG Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips ZLZL ZLZL uL(t)uL(t) 1+ L Delay( ) LL 1+ G GG
Impulse Response 1+ L Delay( ) LL 1+ G GG (t)(t) va(t)va(t) Soonest Response By Reflection & Propagation
Impulse Response 1+ L Delay( ) LL 1+ G GG (t)(t) va(t)va(t)
Impulse Response 1+ L Delay( ) LL 1+ G GG (t)(t) va(t)va(t) 1+ L Delay( ) Delay(2 ) LL 1+ G GG
Impulse Response l=17.5 cm c=350 m/sec =500 Hz = l/c = 0.5 msec
Impulse Response l=17.5 cm c=350 m/sec =500 Hz = l/c = 0.5 msec For nature vowel, resonance frequencies (formants) were approximately 500, 1500, 2500, 3500 Hz.
Digital Simulation for One-Tube Model z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 LL GG 1+ L (1+ G )/2 u G [n]= u G (nT) u L [n]= u L (nT) 1+ L Delay( ) LL 1+ G GG How many sections are required?
Digital Simulation for One-Tube Model Assume L =1, G =1. zMzM zMzM 1 uG[n]uG[n] uL[n]uL[n] z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 LL GG 1+ L (1+ G )/2 u G [n]= u G (nT) u L [n]= u L (nT)
Digital Simulation for One-Tube Model zMzM zMzM 1 uG[n]uG[n] uL[n]uL[n] z-plane
Digital Simulation for One-Tube Model z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 LL GG 1+ L (1+ G )/2 u G [n]= u G (nT) u L [n]= u L (nT) How many sections are required? Voice Band 20~3400 Hz Sampling rate 8000 Hz T = 1/8000 = msec 0.5 msec Glottis Lips 4
Acoustic Tube Modeling (I) Exercises
Exercise z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 LL GG 1+ L (1+ G )/2 u G [n]= u G (nT) u L [n]= u L (nT) M sections Find the transfer function of the above system.
Computer Simulation z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 z1z1 LL GG 1+ L (1+ G )/2 u G [n]= u G (nT) u L [n]= u L (nT) 4 sections Using different G and L and feeding periodic impulse trains with different periods to the system to generate sounds. Plot the generated waveforms.