fs=22050;w1p1=2*pi*850/fs;w1p2=2*pi*950/fs;%归一化截止角频率w1s1=2*pi*750/fs;w1s2=2*pi*1050/fs;%归一化截止角频率w1p1t=tan(w1p1/2);w1p2t=tan(w1p2/2);%预畸数字截止频率，得到模拟滤波器截止频率w1s1t=tan(w1s1/2);w1s2t=tan(w1s2/2);%预畸数字截止频率，得到模拟滤波器截止频率Bw1=w1p2t-w1p1t;%求带通通带Wp1=1;%选择原型模拟低通归一化通带截止频率w10=sqrt(w1p1t*w1p2t);%求通带频率中心Ws1=(w10*w10-w1s1t*w1s1t)/(w1s1t*Bw1);%求原型模拟低通归一化带阻截止频率[N,Wn]=buttord(Wp1,Ws1,1,40,'s');%确定原型模拟低通滤波器的阶数N和截止频率Wn[B,A]=butter(N,Wn,'s');%确定原型模拟低通滤波器[BT,AT]=lp2bp(B,A,w10,Bw1);%对所求出的原型模拟低通滤波器转化为带通滤波器[num,den]=bilinear(BT,AT,0.5);%对其进行双线性变换freqz(num,den)title('频率约为800-1K滤波器');pause[signal,fs,bits]=wavread('login.wav');y1=filter(num,den,signal);sound(y1,fs);pausew2p1=2*pi*1200/fs;w2p2=2*pi*1800/fs;w2s1=2*pi*800/fs;w2s2=2*pi*2200/fs;w2p1t=tan(w2p1/2);w2p2t=tan(w2p2/2);w2s1t=tan(w2s1/2);w2s2t=tan(w2s2/2);Bw2=w2p2t-w2p1t;Wp2=1;w20=sqrt(w2p1t*w2p2t);Ws2=(w20*w20-w2s1t*w2s1t)/(w2s1t*Bw2);[N,Wn]=buttord(Wp2,Ws2,1,40,'s');[B,A]=butter(N,Wn,'s');[BT,AT]=lp2bp(B,A,w20,Bw2);[num,den]=bilinear(BT,AT,0.5);freqz(num,den)title('频率约为1K-2K滤波器');pause[signal,fs,bits]=wavread('login.wav');y2=filter(num,den,signal);sound(y2,fs);pausew3p1=2*pi*2200/fs;w3p2=2*pi*3800/fs;w3s1=2*pi*1800/fs;w3s2=2*pi*4200/fs;w3p1t=tan(w3p1/2);w3p2t=tan(w3p2/2);w3s1t=tan(w3s1/2);w3s2t=tan(w3s2/2);Bw3=w3p2t-w3p1t;Wp3=1;w30=sqrt(w3p1t*w3p2t);Ws3=(w30*w30-w3s1t*w3s1t)/(w3s1t*Bw3);[N,Wn]=buttord(Wp3,Ws3,1,40,'s');[B,A]=butter(N,Wn,'s');[BT,AT]=lp2bp(B,A,w30,Bw3);[num,den]=bilinear(BT,AT,0.5);freqz(num,den)title('频率约为2K-4K滤波器');pause[signal,fs,bits]=wavread('login.wav');y3=filter(num,den,signal);sound(y3,fs);pausew4p1=2*pi*4500/fs;w4p2=2*pi*7500/fs;w4s1=2*pi*3500/fs;w4s2=2*pi*8500/fs;w4p1t=tan(w4p1/2);w4p2t=tan(w4p2/2);w4s1t=tan(w4s1/2);w4s2t=tan(w4s2/2);Bw4=w4p2t-w4p1t;Wp4=1;w40=sqrt(w4p1t*w4p2t);Ws4=(w40*w40-w4s1t*w4s1t)/(w4s1t*Bw4);[N,Wn]=buttord(Wp4,Ws4,1,40,'s');[B,A]=butter(N,Wn,'s');[BT,AT]=lp2bp(B,A,w40,Bw4);[num,den]=bilinear(BT,AT,0.5);freqz(num,den)title('