数字信号处理：用窗函数法设计IIR数字滤波器

实验三：用窗函数法设计IIR数字滤波器

clear all;clc;close all

N=33;wc=pi/2;

hd=ideal(N,wc);

w1=boxcar(N);

w2=hamming(N);

w3=hanning(N);

w4=blackman(N);

h1=hd.*w1';

h2=hd.*w2';

h3=hd.*w3';

h4=hd.*w4';

M=512;

fh1=fft(h1,M);

db1=-20*log10(abs(fh1(1)./(abs(fh1)+eps)));

fh2=fft(h2,M);

db2=-20*log10(abs(fh2(1)./(abs(fh2)+eps)));

fh3=fft(h3,M);

db3=-20*log10(abs(fh3(1)./(abs(fh3)+eps)));

fh4=fft(h4,M);

db4=-20*log10(abs(fh4(1)./(abs(fh4)+eps)));

w=2/M*[0:M-1];

figure

subplot(2,2,1);stem(h1)

subplot(2,2,2);plot(w,abs(fh1))

subplot(2,2,3);plot(w,db1)

subplot(2,2,4);plot(w,angle(fh1))

figure

subplot(2,2,1);stem(h2)

subplot(2,2,2);plot(w,abs(fh2))

subplot(2,2,3);plot(w,db2)

subplot(2,2,4);plot(w,angle(fh2))

figure

subplot(2,2,1);stem(h3)

subplot(2,2,2);plot(w,abs(fh3))

subplot(2,2,3);plot(w,db3)

subplot(2,2,4);plot(w,angle(fh3))

figure

subplot(2,2,1);stem(h4)

subplot(2,2,2);plot(w,abs(fh4))

subplot(2,2,3);plot(w,db4)

subplot(2,2,4);plot(w,angle(fh4))

N1=2048;

t=0:1/256:1/256*(N1-1);

x1=sin(100*pi*t)+sin(200*pi*t)+sin(300*pi*t); figure

subplot(3,2,1);plot(x1(1:100))

F1x1=fft(x1,N1);

w=2/N1*[0:N1-1];

y1=conv(x1,h1);

subplot(3,2,2);plot(w,abs(F1x1))

subplot(3,2,3);plot(y1(1:100))

Fx2=fft(y1,N1)

subplot(3,2,4);plot(w,abs(Fx2))

y2=conv(x1,h4);

subplot(3,2,5);plot(y2(1:100))

Fx3=fft(y1,N1)

subplot(3,2,6);plot(w,abs(Fx3))

矩形窗滤波器：

海明窗滤波器：

汉宁窗滤波器：

布莱克曼窗滤波器：