FFT Filtering of signal

Hi there. I have a signal and I want extract some frequencies like 14 hz. I use some band pass filter like butterworth but answer is not acceptable. And now I want to know how can I use FFT Filter to get my frequency. Best regards.

[Star Strider]

What does not work about your filter?

Post your code, as well as sampling frequency and if possible, attach your signal file or a sample of it.

[Ali Izadi]

Xfft=fft(data); 
FerequencyIndex = round(13*numberofsample/fs)+1;
Zdata=zeros(1,numberof sample);
Zdata(FerequencyIndex) = xfft(FerequencyIndex);
Filterdata=real(iffy(Zdata));

13 is my desire frequency that I want to extract form my signal.

Is it true? For fft filtering?

[Image Analyst]

FerequencyIndexx is different than FerequencyIndex so that should cause an error.

[Ali Izadi]

Sorry. This is prototype of my code. I handle syntax error in my program. In other hand is my algorithm right for filtering by fft?

[Image Analyst]

This will be another error "numberof sample". Do you know there is a way you can copy your code to the clipboard and paste it back here so that you do not need to re-type everything? In Windows you can use Ctrl-c and Ctrl-v.

And what do you mean "extract form"? Do you just want to throw away everything in your data except a perfect sine wave at a frequency of 13? So your output will look like a perfect sine wave?

[Ali Izadi]

My fft filter code :

clc;
clear all;
load('SignalData2');
[n,c] = size(mydata2);
mydata1 = mydata2(1:n,1);

% my sample rate is 39500 or datalenth/4
fs = n/4;      % Sampling rate [Hz]
Ts = 1/fs;       % Sampling period [s]
fNy = fs / 2;    % Nyquist frequency [Hz]
noSamples = n;   % Number of samples
f = 0 : fs/noSamples : fs - fs/noSamples; % Frequency vector

figure;

subplot(2,2,1);
plot(mydata1);
x_fft = abs(fft(mydata1));
subplot(2,2,2);
plot(f,x_fft);
xlim([1 150]);

bw=0.2;      %Bandwisth
fc=pi*14.2;     %Center Frequency
L = n;       % sample number;
%Compute Hamming window
for nn=1:L
    hamm(nn)=(0.54-0.46*cos(2*pi*nn/L));
end
%Compute Filter
hsuup=(-(L-1)/2:(L-1)/2);
hideal1=hamm.*(2*(fc+bw)*(sin(2*(fc+bw)*hsuup/fs)./(2*(2*fc+bw)*hsuup/fs)));
hideal2=hamm.*(2*(fc-bw)*(sin(2*(fc-bw)*hsuup/fs)./(2*(2*fc+bw)*hsuup/fs)));
h_bpf=(hideal1-hideal2);

comp_sig_fft=fft(mydata1)'/L;
h_bpf_fft=fft(h_bpf) /L;
s100_fft=comp_sig_fft.*h_bpf_fft;
band_passed_signal=real(ifft(s100_fft));

subplot(2,2,3);
plot(band_passed_signal);

% 
x_fft = abs(fft(band_passed_signal));
subplot(2,2,4);
plot(f,x_fft);
xlim([1 150]);
   

[Ali Izadi]

This is my data http://wikisend.com/download/428686/SignalData2.mat

[Salaheddin Hosseinzadeh]

is your problem solved now?!

[Ali Izadi]

No. My problem exists yet. If you run code, fft filter result is NaN. I want filter my signal to get 14 hz - 14.4 hz signal.

[Ali Izadi]

I do not know why my code doesn't work properly. I design a band pass filter by hamming windows and fft algorithm to extract 14hz to 14.4hz signal. Is there any idea? Is there any mistake in my code?