求数字滤波的FFT算法实现的MATLAB代码

shuji0414

数字滤波的FFT算法实现的MATLAB代码,谢谢各位了.

[ 本帖最后由 eight 于 2007-5-29 12:19 编辑 ]

octopussheng

我也想要的 啊！！！

tujian510

一些Matalab相关程序！


现发一些自己做毕业设计做的和一些收集到的相关Matalab程序，共大家参考！
Matlab中的fft分析含噪声的信号，其中有直接FFT，时域同步平均后FFT，频域同步平均后FFT

%%This procedure is to investigate the FFT of sine signal, sine signal with
%%noise.  The sine signal with noise is treated by direct FFT,
%%FFT after piece-wise averaging in time domain, and FFT after
%%piece-wise averaging  frequency domain
%%
clear all
pack


w=10;
t=0:(2*pi/w/500):(300*2*pi/w);
x=sin(w*t);

n=length(t);

ss=888;
randn('seed',ss);
z=randn(1,n);
z1=z-mean(z);
z2=z1/max(abs(z1));
z2=z2*500;

figure(1)
plot(t,x)  % The sine signal without noise


fre=(1/(2*pi/w/500))*(1:n)/n;

nn=fix(n/2);
y1=fft(x);  % The FFT of sine signal without noise
y1=(abs(y1)).^2/n;
y2=y1(2:(nn+1));
fre1=2*pi*fre(1:nn);

figure(2)
plot(fre1,y2)

x=x+z2;

y1=fft(x);  % The FFT of sine signal with noise
y1=(abs(y1)).^2/n;
y2=y1(2:(nn+1));

figure(3)
plot(fre1,y2)         %The sine signal with noise

%% Averaging in time domain

M=10000;
xx=zeros(1,M);
m1=1;m2=M;

nnnn=fix(300*500/M);

for nnn=1:nnnn
    xxx=x(m1:m2);
    xx=xx+xxx;
    m1=m1+M;
    m2=m2+M;
end

fre=(1/(2*pi/w/500))*(1:M)/M;

nn=fix(M/2);
xx=xx/nnnn;
y1=fft(xx);
y1=(abs(y1)).^2/M;
y2=y1(2:(nn+1));
fre1=2*pi*fre(1:nn);

figure(4)
plot(fre1,y2)



% Next is averaging in frequency domain
% In fact, the averaging in time domain is identical with that in frequency
% domain

MM=10000;
xx=zeros(1,MM);
m1=1;m2=MM;

nnnn=fix(300*500/MM);

for nnn=1:nnnn
    xxx=x(m1:m2);
    xxx=fft(xxx);
    %xxx=sqrt((abs(xxx)).^2);
    xx=xx+xxx;
    m1=m1+MM;
    m2=m2+MM;
end

y1=xx/nnnn;
y1=(abs(y1)).^2/MM;


fre=(1/(2*pi/w/500))*(1:MM)/MM;

nn=fix(MM/2);
y2=y1(2:(nn+1));
fre1=2*pi*fre(1:nn);

figure(5)
plot(fre1,y2)


对余弦信号的FFT分析程序:
%f—余弦信号的频率

% M—基2 FFT幂次数 N=2^M为采样点数，这样取值是为了便于作基2的FFT分析

%2. 采样频率Fs

%*******************************************************************%

function samples(f,Fs,M)

N=2^M; % fft点数=取样总点数

Ts=1/Fs; % 取样时间间隔

T=N*Ts; % 取样总时间=取样总点数*取样时间间隔

n=0:N-1;

t=n*Ts;

Xn=cos(2*f*pi*t);

subplot(2,1,1);

stem(t,Xn);

axis([0 T 1.1*min(Xn) 1.1*max(Xn)]);

xlabel('t -->');

ylabel('Xn');

Xk=abs(fft(Xn,N));

subplot(2,1,2);

stem(n,Xk);

axis([0 N 1.1*min(Xk) 1.1*max(Xk)]);

xlabel('frequency -->');

ylabel('!Xk!');

tujian510

可以参考http://forum.vibunion.com/forum/thread-44622-1-1.html

ztx106

很好的学习资料，楼主有做傅里叶逆变换然后再FFT变换的例子没有啊？传上来学习下