%有四种窗口类型供选择
b=1;
close all;
i=0;
while(b);
temp=menu('选择窗函数长度N','N=10','N=15','N=20','N=25','N=30','N=33','N=35','N=40','N=45','N=50','N=55','N=60','N=64');
menu1=[10,15,20,25,30,33,35,40,45,50,55,60,64];
N=menu1(temp);
temp=menu('选择逼近理想低通滤波器截止频率Wc','Wc=pi/4','Wc=pi/2','Wc=3*pi/4','Wc=pi','Wc=0.5','Wc=1.0','Wc=1.5','Wc=2.0','Wc=2.5','Wc=3.0');
menu2=[pi/4,pi/2,3*pi/4,pi,0.5,1,1.5,2,2.5,3];
w=menu2(temp);
n=[0
N-1)];
hd=ideal(w,N); %得到理想低通滤波器
k=menu('请选择窗口类型:','boxcar','hamming','hanning','blackman');
if k==1
B=boxcar(N);
string=['Boxcar','N=',num2str(N)];
else if k==2
B=hamming(N);
string=['Hamming','N=',num2str(N)];
else if k==3
B=hanning(N);
string=['Hanning','N=',num2str(N)];
else if k==4
B=blackman(N);
string=['Blackman','N=',num2str(N)];
end
end
end
end
h=hd.*(B)'; %得到FIR数字滤波器
[H,m]=freqz(h,[1],1024,'whole'); %求其频率响应
mag=abs(H); %得到幅值
db=20*log10((mag+eps)/max(mag));
pha=angle(H); %得到相位
i=i+1;
figure(i)
subplot(2,2,1);
n=0:N-1;
stem(n,h,'.');
axis([0,N-1,-0.1,0.3]);
hold on;
n=0:N-1;
x=zeros(N);
plot(n,x,'-');
xlabel('n');
ylabel('h(n)');
title('实际低通滤波器的h(n)');
text((0.3*N),0.27,string);
hold off;
subplot(2,2,2);
plot(m/pi,db);
axis([0,1,-100,0]);
xlabel('w/pi');
ylabel('dB');
title('衰减特性(dB)');
grid;
subplot(2,2,3);
plot(m,pha);
hold on;
n=0:7;
x=zeros(8);
plot(n,x,'-');
title('相频特性');
xlabel('频率(rad)');
ylabel('相位(rad)');
axis([0,3.15,-4,4]);
subplot(2,2,4);
plot(m,mag);
title('频率特性');
xlabel('频率W(rad)');
ylabel('幅值');
axis([0,3.15,0,1.5]);
text(0.9,1.2,string);
b=menu('Do You want To Continue ?','Yes','No');
if b==2
b=0;
end
end
temp=menu('Close All Figure ?','Yes','No');
if temp==1
close all
end