ws1=0.3*pi;
wp1=0.45*pi;
wp2=0.65*pi;
ws2=0.75*pi;
As=40;
tr_width=min((wp1-ws1),(ws2-wp2));
M=ceil(11.*pi/tr_width)+1;
n=[0:1:M-1];
wc1=(ws1+wp1)/2;
wc2=(wp2+ws2)/2;


hd=ideal_lp(wc2,M) - ideal_lp(wc1,M);
w_bla=(blackman(M))';
h=hd.*w_bla;
[db,mag,pha,grd,w]=freqz_m(h,[1]);
delta_w=2*pi/1000;
Rp=-min(db(wp1/delta_w+1:1:wp2/delta_w))
As=-round(max(db(ws2/delta_w+1:1:501)));

figure(1);
subplot(2,2,1);stem(n,hd);title('ideal impulse response')
axis([0 M-1 -0.4 0.5]);ylabel('hd(n)')
subplot(2,2,2);plot(w/pi,pha);grid
xlabel('freq(uni：\pi)');ylabel('xiangwei');
title('IIR xiangwei');
subplot(2,2,3);stem(n,w_bla);title('blackmanwindow')
axis([0 M-1 0 1.1]);ylabel('h(n)')
subplot(2,2,4);plot(w/pi,db);
title('magnitude response in db');
grid;
ylabel('decibels')
axis([0 1 -150 10]);
set(gca,'xtickmode','manual','xtick',[0,0.2,0.35,0.65,0.8,1])
set(gca,'ytickmode','manual','ytick',[-60,0])
set(gca,'yticklabelmode','manual','yticklables',['60';'0'])