clear all,clc
Fs=200e3;
Ts=1/Fs;
t=0:Ts:5e-3-Ts;

f1=1e3;
f2=20e3;
f3=30e3;

y=5*sin(2*pi*f1*t)+5*sin(2*pi*f2*t)+10*sin(2*pi*f3*t);
% plot(t,y)
nfft=2^nextpow2(length(y));
fy=fft(y,nfft);
fy=fy(1:nfft/2);
xfft=Fs*(0:nfft/2-1)/nfft;

% plot(xfft,abs(fy))
% plot(xfft,abs(fy)/max(abs(fy)))

cutoff=1.5e3/Fs/2;
order=32;
h=fir1(order,cutoff,hamming(order+1));

fh=fft(h,nfft);
fh=fh(1:nfft/2);
mul=fh.*fy;
% plot(abs(mul/max(mul)))

subplot(3,1,1)
plot(xfft,abs(fy/max(fy)))
subplot(3,1,2)
plot(xfft,abs(fh/max(fh)))
subplot(3,1,3)
plot(xfft,abs(mul/max(mul)))