wp1 = 0.35*pi; wp2 = 0.45*pi; 
ws1 = 0.3*pi; ws2 = 0.5*pi;
As =20; Ap=3;
tr_width = min((wp1-ws1),(ws2-wp2)) % 1)過渡帶寬
n=[0:45]; 
wc1 = (ws1+wp1)/2; wc2 = (wp2+ws2)/2; %2) 截止頻率2個
hd= ideal_lp(wc2,46) -ideal_lp(wc1,46); % 3)hd(n)
w_bla= (boxcar(46))';                % 4) w(n)
h = hd.* w_bla;                       % 5) h(n)
[db,mag,pha,grd,w] = freqz_m(h,[1]);  % 6) h(n)頻譜計算
delta_w = 2*pi/1000;
Rp= -min(db(wp1/delta_w+1:1:wp2/delta_w))         %7) MAX Rp
As = -round(max(db(ws2/delta_w+1:1:501)))         %7) Min As
subplot(2,2,1); 
stem(n,hd); title('理想沖擊響應') 
axis([0 50 -0.4 0.5]); xlabel('n'); ylabel('hd(n)')
subplot(2,2,2);
stem(n,w_bla);title('45點矩形窗') 
axis([0 50 0 1.1]);  ylabel('w(n)')
subplot(2,2,3);
stem(n,h);title('實際沖擊響應')
axis([0 50 -0.4 0.5]); ylabel('h(n)')
subplot(2,2,4);
plot(w/pi,db);title('衰減幅度');
axis([0 1 -150 50]); ylabel('Decibels')
grid;