1、实验2数字信号处理wp=2*1000*tan(2*pi*300/(2*1000);ws=2*1000*tan(2*pi*200/(2*1000);N,wn=cheb1ord(wp,ws,0.8,20,s);B,A=cheby1(N,0.8,wn,s);bn1,an1=bilinear(B,A,2000);h,w=freqz(bn1,an1);f=w/pi*500;plot(f,20*log10(abs(h);axis(0,500,-30,10);grid on;xlabel(频率);ylabel(幅度响应);wp=2*1000*tan(2*pi*200/(2*1000);ws=2*1000*t
2、an(2*pi*300/(2*1000);Ap=1;As=25;n,Wn=buttord(Wp,Ws,Ap,As,s);b,a=butter(n,Wn,s);bn1,an1=bilinear(b,a,1000);H1,W=freqz(bn1,an1);bn2,an2=impinvar(b,a,1000);H2,W=freqz(bn2,an2);f=W/(2*pi)*1000;plot(f,abs(H1),-.,f,abs(H2),-);grid onxlabel(频率);ylabel(幅度响应);legend(双线性变法,脉冲响应不变法);wp=2*8000*tan(2*pi*1200/(2*
3、8000);ws=2*8000*tan(2*pi*2000/(2*8000);N1,wn1=buttord(wp,ws,0.5,40,s);B1,A1=butter(N1,wn1,s);bn1,an1=bilinear(B1,A1,8000);h1,w1=freqz(bn1,an1);f1=w1/(2*pi)*8000;subplot(311);plot(f1,20*log10(abs(h1);axis(0,4000,-80,10);grid on;xlabel(频率1);ylabel(幅度响应1);title(butterworth滤波器);N2,wn2=cheb1ord(wp,ws,0.5
4、,40,s);B2,A2=cheby1(N2,0.5,wn2,s);bn2,an2=bilinear(B2,A2,8000);h2,w2=freqz(bn2,an2);f2=w2/(2*pi)*8000;subplot(312);plot(f2,20*log10(abs(h2);axis(0,4000,-80,10);grid on;xlabel(频率2);ylabel(幅度响应2);title(chebyshev滤波器);N3,wn3=ellipord(wp,ws,0.5,40,s);B3,A3=ellip(N3,0.5,40,wn3,s);bn3,an3=bilinear(B3,A3,80
5、00);h3,w3=freqz(bn3,an3);f3=w3/(2*pi)*8000;subplot(313);plot(f3,20*log10(abs(h3);axis(0,4000,-80,10);grid on;xlabel(频率3);ylabel(幅度响应3);title(椭圆滤波器);w1=2*30000*tan(2*pi*2000/(2*30000);w2=2*30000*tan(2*pi*3000/(2*30000);wr1=2*30000*tan(2*pi*1500/(2*30000);wr2=2*30000*tan(2*pi*6000/(2*30000);N,wn=butto
6、rd(w1 w2,wr1 wr2,3,20,s);B,A=butter(N,wn,s);bn1,an1=bilinear(B,A,30000);h,w=freqz(bn1,an1);f=w/(2*pi)*30000;plot(f,20*log10(abs(h);axis(0,15000,-80,10);grid on;xlabel(频率3);ylabel(幅度响应3);N=45，计算并画出矩形窗、汉明窗、布莱克曼窗的归一化的幅度谱，并比较各自的主要特点。N=45;wn1=kaiser(N,0);wn2=hamming(N);wn3=blackman(N);h1,w1=freqz(wn1,N);
7、h2,w2=freqz(wn2,N);h3,w3=freqz(wn3,N);plot(w1/pi,20*log10(abs(h1),-,w2/pi,20*log10(abs(h2),-,w3/pi,20*log10(abs(h3),:);axis(0,1,-120,10);grid;xlabel(归一化频率/pi);ylabel(幅度/dB);title(三种窗口函数);legend(矩形窗,汉明窗,布莱克曼窗,3);N=15;h=fir1(N-1,0.3 0.5,bandpass,hanning(N);h1,w1=freqz(h,1);subplot(2,1,1);plot(w1/pi,20
8、*log10(abs(h1);axis(0,1,-80,10);grid;xlabel(频率/pi);ylabel(幅度/dB);title(N=15,矩形窗);N=45;h=fir1(N-1,0.3 0.5,bandpass,hanning(N);h1,w1=freqz(h,1);subplot(2,1,2);plot(w1/pi,20*log10(abs(h1);axis(0,1,-80,10);grid;xlabel(频率/pi);ylabel(幅度/dB);title(N=45,矩形);N=15;h=fir1(N-1,0.3 0.5,bandpass,hanning(N);figure
9、(1)freqz(h,1)title(N=15,汉宁窗);N=45;h=fir1(N-1,0.3 0.5,bandpass,hanning(N);figure(2)freqz(h,1)title(N=45,汉宁窗);将上式的hanning 改为下面的形式%矩形窗N=15;h=fir1(N-1,0.3 0.5,bandpass,boxcar(N);h1,w1=freqz(h,1);subplot(2,1,1);plot(w1/pi,20*log10(abs(h1);axis(0,1,-80,10);grid;xlabel(频率/pi);ylabel(幅度/dB);title(N=15,矩形窗);
10、N=45;h=fir1(N-1,0.3 0.5,bandpass,boxcar(N);h1,w1=freqz(h,1);subplot(2,1,2);plot(w1/pi,20*log10(abs(h1);axis(0,1,-80,10);grid;xlabel(频率/pi);ylabel(幅度/dB);title(N=45,矩形);N=15;h=fir1(N-1,0.3 0.5,bandpass,blackman(N);h1,w1=freqz(h,1);subplot(2,1,1);plot(w1/pi,20*log10(abs(h1);axis(0,1,-80,10);grid;xlabe
11、l(频率/pi);ylabel(幅度/dB);title(N=15,布莱克曼窗);N=45;h=fir1(N-1,0.3 0.5,bandpass,blackman(N);h1,w1=freqz(h,1);subplot(2,1,2);plot(w1/pi,20*log10(abs(h1);axis(0,1,-80,10);grid;xlabel(频率/pi);ylabel(幅度/dB);title(N=45,布莱克曼窗);如：N=40;f=0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 1;a=0 0 1 1 0 0 1 1 0 0;beta=4;h=fir2(N-1,f
12、,a,kaiser(N,beta);h1,w1=freqz(h,1);subplot(3,1,1);plot(w1/pi,20*log10(abs(h1);axis(0,1,-80,10);grid;xlabel(频率/pi);ylabel(幅度/dB);title(beta=4时凯泽窗专用线性相位滤波器);beta=6;h=fir2(N-1,f,a,kaiser(N,beta);h1,w1=freqz(h,1);subplot(3,1,2);plot(w1/pi,20*log10(abs(h1);axis(0,1,-80,10);grid;xlabel(频率/pi);ylabel(幅度/dB
13、);title(beta=6时凯泽窗专用线性相位滤波器);beta=10;h=fir2(N-1,f,a,kaiser(N,beta);h1,w1=freqz(h,1);subplot(3,1,3);plot(w1/pi,20*log10(abs(h1);axis(0,1,-80,10);grid;xlabel(频率/pi);ylabel(幅度/dB);title(beta=10时凯泽窗专用线性相位滤波器);第四题f = 0 0.5 0.5 1; m = 1 1 0 0;b = fir2(63,f,m);h,w = freqz(b,1,128);plot(f,m,w/pi,abs(h)legend(Ideal,fir2 Designed)title(频率采样的低通滤波器)
