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>----------------------------------------------------------------------------
> exa030201, for example 3.2.1 and fig 3.2.3;
> to show Gibbs phenomena;
>----------------------------------------------------------------------------
clear;
wc=0.6*pi;a=[1];Nf=256;
Hd1=ones(1,0.6*Nf+1);
Hd2=zeros(1,0.4*Nf);
Hd=[Hd1,Hd2]';
> 改变窗函数的长度，观察Gibbs现象
>
M=10; > for M=10
N=2*M+1;
for n=1:N
if (n-M)==0;
h(n)=wc/pi;
else
h(n)=sin(wc*(n-M))/(pi*(n-M));
end
end
[H,w]=freqz(h,a,Nf,1);
subplot(221)
plot(w,Hd,'-',w,abs(H));grid on;
>
M=30; > for M=30
N=2*M+1;
for n=1:N
if (n-M)==0;
h(n)=wc/pi;
else
h(n)=sin(wc*(n-M))/(pi*(n-M));
end
end
[H,w]=freqz(h,a,Nf,1);
subplot(222)
plot(w,Hd,'-',w,abs(H));grid on;
>
M=50; >for M=50
N=2*M+1;
for n=1:N
if (n-M)==0;
h(n)=wc/pi;
else
h(n)=sin(wc*(n-M))/(pi*(n-M));
end
end
[H,w]=freqz(h,a,Nf,1);
subplot(223)
plot(w,Hd,'-',w,abs(H));grid on;
>
M=100; > for M=100
N=2*M+1;
for n=1:N
if (n-M)==0;
h(n)=wc/pi;
else
h(n)=sin(wc*(n-M))/(pi*(n-M));
end
end
[H,w]=freqz(h,a,Nf,1);
subplot(224)
plot(w,Hd,'-',w,abs(H));grid on;