ex_07_04_1.m

是属于清华大学出的书 数字信号处理及电子课件光盘内容

%  ex_07_04_1.m :  习题 7.4

clear all;
close all;
N=33;
m=(N-1)/4;
n=1:N;
h(n)=0;
for k=0:(m-1)
    n=4*k+2;
    h(n+1)=8/(pi*(n-16))/(pi*(n-16));
end
h((N+1)/2)=0.5;

 
for k=0:(N-1)/2
    w1(k+1)=0.5-0.5*cos(2*pi*(k-16)/N);
end
w2=fliplr(w1);
w=[w2(1:end-1) w1];
hw=h.*w;
%
subplot(221);stem(hw,'.k');grid on;
h1=freqz(hw,1,N);
t=0:1/N/2:1-1/N/2;
subplot(222);plot(t,[abs(h1)' abs(h1)']);grid;


clear all;
N=33;
factor=(N+1)/2;
j=sqrt(-1);
 
for k=0:(N-1)   
m=pi*k/(factor-1);
    if(m<=pi/2)
        Hd(k+1)=-2/pi*m+1;
    elseif((m>pi/2)&&(m<=pi))
            Hd(k+1)=2/pi*m-1;
    elseif(m>pi)
            Hd(k+1)=Hd(N-k+1);
    end
end
for k=0:(N-1)
   a=-j*(N-1)*k*pi/N;
   H(k+1)=exp(a)*Hd(k+1);
end
 
for i=0:(N-1)
    s=0;
    for k=0:(N-1)
        a=j*2*pi*i*k/N;
        s=s+H(k+1)*exp(a);
    end
    h(i+1)=s/N;
end
h=real(h);
subplot(223);stem(h,'.k');grid on;
h1=freqz(h,1,N);
t=0:1/N/2:1-1/N/2;
subplot(224)
plot(t,[abs(h1)' abs(h1)']);grid;
axis([0 1 0 1]);