w=-4*pi:2*pi/255:4*pi;
x1=[1 3 5 7 9 11 13 15 17];
x2=[1 -1 1 -1 1 -1 1 -1 1];
y=x1.*x2;
h1=freqz(x1,1,w);
h2=freqz(x2,1,w);
h3=freqz(y,1,w);
h4=conv(h1,h2)/2/pi;
subplot(4,1,1)
plot(w,abs(h1))
title('first serials a-w curve')
subplot(4,1,2)
plot(w,abs(h2))
title('second serials a-w curve')
subplot(4,1,3)
plot(w,abs(h3))
title('x1.x2 a-w curve')
subplot(4,1,4)
plot(w,abs(h4(510:1530)))
title('convolution')