用升余弦窗设计一线性相位低通FIR数字滤波器.doc

用升余弦窗设计一线性相位低通FIR数字滤波器N=15时：n=0:14;n1=n-7;nn=n1+(n1=0)*eps;hd=sin(pi/4*nn)./(pi*nn);title(N=15 h1);h1=hd.*(hanning(15);subplot(4,1,1);stem(n,h,.); axis(0,14,-0.1,0.3);h11,m=freqz(h1,1,1024);mag=abs(h11);ang=angle(h11);mag1=mag/max(mag);subplot(4,1,2);plot(m,mag1,k);axis(0,3.5,-0.1,1.2);title(N=15 幅频特性 );subplot(4,1,3);plot(m,ang,k);title(N=15 相位特性);a=20*log10(mag1)；subplot(4,1,4);plot(m,a,k);axis(0,3.5,-120,20);title(N=15 衰减特性);N=33时：n=0:32;n1=n-16;nn=n1+(n1=0)*eps;hd=sin(pi/4*nn)./(pi*nn); h1=hd.*(hanning(33);subplot(4,1,1);stem(n,h1,k.); axis(0,32,-0.1,0.3); title(N=33 h1); h11,m=freqz(h1,1,1024);mag=abs(h11);ang=angle(h11);mag1=mag/max(mag);subplot(4,1,2);plot(m,mag1,k);axis(0,3.5,-0.1,1.2);title(N=33 幅频特性);subplot(4,1,3);plot(m,ang,k);title(N=33 相位特性);a=20*log10(mag1);subplot(4,1,4);plot(m,a,k);axis(0,3.5,-150,20);title(N=33 衰减特性);用四种窗函数设计线性相位低通滤波器n=0:32;n1=n-16;nn=n1+(n1=0)*eps;hd=sin(pi/4*nn)./(pi*nn);h1=hd;h11,m=freqz(h1,1,1024);mag=abs(h11);mag1=mag/max(mag);a1=20*log10(mag1);subplot(4,2,1);plot(m,mag1,k); axis(0,3.5,-0.1,1.2); title(矩形窗幅频特性);subplot(4,2,2);plot(m,a1,k);axis(0,3.5,-150,20);title(矩形窗衰减特性);h2=hd.*(boxcar(33);h22,m=freqz(h2,1,1024);mag=abs(h22);mag2=mag/max(mag);a2=20*log10(mag2);subplot(4,2,3);plot(m,mag2,k); axis(0,3.5,-0.1,1.2); title(三角窗幅频特性);subplot(4,2,4);plot(m,a2,k);axis(0,3.5,-150,20);title(三角窗衰减特性);h3=hd.*(hamming(33);h33,m=freqz(h3,1,1024);mag=abs(h33);mag3=mag/max(mag);a3=20*log10(mag3);subplot(4,2,5);plot(m,mag3,k); axis(0,3.5,-0.1,1.2);title(汉宁窗幅频特性);subplot(4,2,6);plot(m,a3,k);axis(0,3.5,-150,20);title(汉宁窗衰减特性);h4=hd.*(hanning(33);h44,m=freqz(h4,1,1024);mag=abs(h44);mag4=mag/max(mag);a4=20*log10(mag4);subplot(4,2,7);plot(m,mag4,k); axis(0,3.5