% 《數字信號處理教程——MATLAB釋義與實現》第四章演示程序
%  電子工業出版社出版  陳懷琛編著 2004年9月
%  數字濾波器頻帶變換演示
%  call_dlp2bp.m 數字低通濾波器到數字帶通濾波器
%
function []=call_dlp2bp(h1,h2)
axes(h1);hold off;
plot([0,0],[-1.2,1.2],'linestyle','-.','color','g');hold on
plot([-1.2,1.2],[0,0],'linestyle','-.','color','g');axis([-1.2,1.2,-1.2,1.2]);
axes(h2);hold off;
plot([0,0],[-1.2,1.2],'linestyle','-.','color','g');hold on
plot([-1.2,1.2],[0,0],'linestyle','-.','color','g');axis([-1.2,1.2,-1.2,1.2]);

w0=0.2*pi;   %低通濾波器的截止頻率(指過渡濾波器，而非最終要設計的濾波器，它的截止頻率在wc（dtransform.m中)設置
w=-pi:0.1:pi;%在這里可以更改其間隔,如果改成0:0.1:2*pi,則下面的判斷要改成abs(w(i))<w0  | abs(w(i))>2*pi-w0
zlp=exp(j*w);

[zbp0,zbp1]=dtransform(w,'lp2bp');

mark1=1;mark2=1;

for j=1:2
    for i=1:length(w)
        %繪制低通濾波器
        axes(h1);
        if (j==2 & mark1==1)
        mark1=0;
        hold off;
        plot([0,0],[-1.2,1.2],'linestyle','-.','color','g');hold on
        plot([-1.2,1.2],[0,0],'linestyle','-.','color','g');axis([-1.2,1.2,-1.2,1.2]);

        end
        if (abs(w(i))<w0)
            plot(zlp(i),'linestyle','o','color','r');axis([-1.2,1.2,-1.2,1.2]);axis('equal');hold on
        else
            plot(zlp(i),'linestyle','o','color','b');axis([-1.2,1.2,-1.2,1.2]);axis('equal');hold on
        end
        
        %繪制帶通濾波器
        axes(h2);
        if (j==2)
           if (abs(w(i))<w0)
            plot(zbp0(i),'linestyle','o','color','r');axis([-1.2,1.2,-1.2,1.2]);axis('equal');hold on
           else
             plot(zbp0(i),'linestyle','o','color','b');axis([-1.2,1.2,-1.2,1.2]);axis('equal');hold on
           end
         else
            if (abs(w(i))<w0)
            plot(zbp1(i),'linestyle','o','color','r');axis([-1.2,1.2,-1.2,1.2]);axis('equal');hold on
           else
             plot(zbp1(i),'linestyle','o','color','b');axis([-1.2,1.2,-1.2,1.2]);axis('equal');hold on
           end
         end
        pause(0.2);
      end
      pause(0.5);
end