function?Hd?=?untitled
%UNtitleD?Returns?a?discrete-time?filter?object.
f1=5;f2=10;f3=20;
N=200;Fs=100;n=0:N-1;Ts=1/Fs;t=n*Ts;
s=sin（2*pi*f1*t）+sin（2*pi*f2*t）+sin（2*pi*f3*t）;
figure（1）;hold?on;plot（ts）;
nfft=200;
Y=fft（snfft）/sqrt（N-1）;f=（0:nfft-1）*Fs/nfft;
figure（2）;hold?on;stem（f（1:N/2）abs（Y（1:N/2）））
grid?on
%
%?MATLAB?Code
%?Generated?by?MATLAB（R）?8.0?and?the?Signal?Processing?Toolbox?6.18.
%
%?Generated?on:?03-Jun-2014?16:12:04
%

%?Butterworth?Bandpass?filter?designed?using?FDESIGN.BANDPASS.

%?All?frequency?values?are?in?Hz.
Fs?=?200;??%?Sampling?Frequency

Fstop1?=?6;???????????%?First?Stopband?Frequency
Fpass1?=?8;???????????%?First?Pass