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% exa070502.m  for example 7.5.2 and fig 7.5.2 
% 本程序说明如何利用两通道滤波器组实现信号的分解和重建； 
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clear all 
load h0;  % h0 是由 exa070501.m 设计出的低通分析滤波器； 
h1=qmf(h0,1); 
g0=-wrev(h0); 
g1=qmf(g0); 
 
fs=200;f1=5;f2=20; 
N=1000;n=1:N; 
Sig1=2*sin(2*pi*f1*n/fs); 
Sig2=2*sin(2*pi*f2*n/fs); 
P1=var(Sig1+Sig2) 
Nos=0.2*randn(N,1); 
P2=var(Nos); 
snr=10*log10(P1/P2) 
Sig=Sig1'+Sig2'+Nos; 
% Sig 是试验信号，它由两个实正弦加白噪声组成，信噪比约为20dB; 
 
% 2.   signal v0(n) and v1(n) after decompositon and decimation 
x0=filter(h0,1,Sig); 
v0=decimate(x0,2); %low pass 
x1=filter(h1,1,Sig); 
v1=decimate(x1,2);  % high pass 
 
% 3.   reconstructed signal by filter  [g0(n) g1(n)] 
u0=interp(v0,2); 
u1=interp(v1,2); 
x_recon=filter(g0,1,u0)+filter(g1,1,u1); 
 
subplot(311) 
plot(Sig(45:165));grid; 
subplot(312) 
plot(x_recon(50:170));grid; 
subplot(313) 
plot(Sig(45:165),'k');grid; 
hold on 
plot(x_recon(50:170),'b');