fs=8000;
t=0:1/fs:1;
x1=4*cos(2*pi*400*t);
x2=4*cos(2*pi*900*t+0.5*pi);
x3=5*cos(2*pi*400*t+0.25*pi);
xt=x1+x2+x3;

a=1;
bLP =[ 
-0.0012 -0.0025 -0.0045 -0.0068 -0.0073 -0.0030 0.0089 ... 
0.0297 0.0583 0.0907 0.1208 0.1422  0.1500 0.1422 ...
0.1208 0.0907 0.0583 0.0297 0.0089 -0.0030 -0.0073 ... 
-0.0068 -0.0045 -0.0025 -0.0012];
bBP =[ 
0.0004 -0.0017 -0.0064 -0.0076 0.0073  0.0363 0.0458 ... 
0.0000 -0.0802 -0.1134 -0.0419 0.0860  0.1500 0.0860 ...
-0.0419 -0.1134 -0.0802 0.0000 0.0458  0.0363 0.0073 ... 
-0.0076 -0.0064 -0.0017 0.0004 ];

figure(1)
freqz(bLP,a,512,fs);
figure(2)
freqz(bBP,a,512,fs);

y1=filter(bBP,a,xt);
Ak1=abs(fft(y1))/length(y1);
k1=0:1:length(y1)-1;
f1=k1*fs/length(y1);

y2=filter(bLP,a,xt);
Ak2=abs(fft(y2))/length(y2);
k2=0:1:length(y2)-1;
f2=k2*fs/length(y2);

Ak3=abs(fft(xt))/length(xt);
k3=0:1:length(xt)-1;
f3=k3*fs/length(xt);

figure(3)
subplot(3,1,1)
plot(f3,Ak3)
title('x(t)')
subplot(3,1,2)
plot(f1,Ak1)
title('band pass untuk y1')
subplot(3,1,3)
plot(f2,Ak2)
title('low pass untuk y2')