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Acoustic Tube Modeling (I) 虞台文
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Content Introduction Wave Equations for Lossless Tube Uniform Lossless Tube Lips-Radiation Model Glottis Model One-Tube Vocal Tract Model Exercises
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Acoustic Tube Modeling (I) Introduction
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Vocal Tract
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Acoustic Tube Derivation Lips Glottis
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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.
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Discrete Area Functions Lips Glottis Area Lips Glottis
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Acoustic Tube Modeling (I) Wave Equations for Lossless Tube
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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
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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
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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
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Vocal Tract A(x, t) x=0x=lx=l GlottisLips u(x,t)u(x,t) p(x,t)p(x,t)
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Acoustic Tube Modeling (I) Uniform Lossless Tube
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Uniformly Lossless Tube x=0x=lx=l
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Uniformly Lossless Tube x=0x=lx=l
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Uniformly Lossless Tube x=0x=lx=l
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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)
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Pressure vs. Volume Flow
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0 Characteristic Impedance of the tube.
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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
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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
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Acoustic Tube Modeling (I) Lips-Radiation Model
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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
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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
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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)
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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)
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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
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Acoustic Tube Modeling (I) Glottis Model
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Boundary Condition (Glottis) uG(t)uG(t) ZGZG ZGZG Tube (Vocal Tract) Tube (Vocal Tract) GlottisLips
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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
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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
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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
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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
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Acoustic Tube Modeling (I) One-Tube Vocal Tract Model
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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
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Impulse Response 1+ L Delay( ) LL 1+ G GG (t)(t) va(t)va(t) Soonest Response By Reflection & Propagation
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Impulse Response 1+ L Delay( ) LL 1+ G GG (t)(t) va(t)va(t)
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Impulse Response 1+ L Delay( ) LL 1+ G GG (t)(t) va(t)va(t) 1+ L Delay( ) Delay(2 ) LL 1+ G GG
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Impulse Response l=17.5 cm c=350 m/sec =500 Hz = l/c = 0.5 msec
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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.
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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?
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Digital Simulation for One-Tube Model Assume L =1, G =1. zMzM zMzM 11 1 2 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)
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Digital Simulation for One-Tube Model zMzM zMzM 11 1 2 1 uG[n]uG[n] uL[n]uL[n] z-plane
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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 = 0.125 msec 0.5 msec Glottis Lips 4
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Acoustic Tube Modeling (I) Exercises
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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.
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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.
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