% 第七章: 例 7.14
% 頻率采樣技術: 低通，樸素法
%
M = 20; alpha = (M-1)/2; l = 0:M-1; wl = (2*pi/M)*l;
Hrs = [1,1,1,zeros(1,15),1,1];
Hdr = [1,1,0,0]; wdl = [0,0.25,0.25,1];
k1 = 0:floor((M-1)/2); k2 = floor((M-1)/2)+1:M-1;
angH = [-alpha*(2*pi)/M*k1, alpha*(2*pi)/M*(M-k2)];
H = Hrs.*exp(j*angH);
h = real(ifft(H,M));
[db,mag,pha,grd,w] = freqz_m(h,1);
[Hr,ww,a,L] = Hr_Type2(h);
subplot(1,1,1)
subplot(2,2,1);plot(wl(1:11)/pi,Hrs(1:11),'o',wdl,Hdr); 
axis([0,1,-0.1,1.1]); title('頻率樣本: M=20')
xlabel(''); ylabel('Hr(k)')
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1])
set(gca,'YTickMode','manual','YTick',[0,1]); grid
subplot(2,2,2); stem(l,h); axis([-1,M,-0.1,0.3])
title('脈沖響應');ylabel('h(n)');text(M+1,-0.1,'n')
subplot(2,2,3); plot(ww/pi,Hr,wl(1:11)/pi,Hrs(1:11),'o');
axis([0,1,-0.2,1.2]); title('振幅響應')
xlabel('頻率（單位：pi）'); ylabel('Hr(w)')
set(gca,'XTickMode','manual','XTick',[0,0.2,0.3,1])
set(gca,'YTickMode','manual','YTick',[0,1]); grid
subplot(2,2,4);plot(w/pi,db); axis([0,1,-200,10]); grid
title('幅度響應'); xlabel('頻率（單位：pi）');
ylabel('分貝數');
set(gca,'XTickMode','Manual','XTick',[0;0.2;0.3;1]);
set(gca,'YTickMode','Manual','YTick',[-16;0]);
set(gca,'YTickLabelMode','manual','YTickLabels',['16';' 0'])
%