Low pass Filter - designing one

Hi there I am currently trying to perform FFT on an acceleration signal. I have values in terms of g values, ie 0.95g etc.

I have produced a FFT plot using the following code and the Hamming window

clc
clear all;
x1=load('TEXT PILOT CC LANKLE_converted_1.txt');
 x=x1(:,1);
  win = hamming(length(x));
  %win=ones(length(x),1);
 y=x.*win;
NFFT = 2.^nextpow2(length(x));
FFTX = fft(y,NFFT)/length(x);
Fs=60;
figure(3)
%plotting
f = Fs/2*linspace(0,1,NFFT/2+1);
cyclespersecond=2*abs(FFTX(1:NFFT/2+1));
% Plot single-sided amplitude spectrum.
plot(f,2*abs(FFTX(1:NFFT/2+1))) 
title('Single-Sided Amplitude Spectrum of y(t)')
xlabel('Frequency (Hz)')
ylabel('|Y(f)|')

I get a high spike at 0 and was thinking this could be due to G. I want to look at walking running etc and so I dont want to get rid of many low frequencies just this high one as I can barely see the other peaks in the spectrum as a result. I thought of using a low pass filter but really dont know where to start in designing them as I have never used it before. Also I was wondering if subtracting the mean would make my peaks more clear?

Also could this poor spectrum be due to lots of noise?

Any help or advice would be appreciated.

[Jeremy]

The high spike at zero is present because of the DC (frequency = 0Hz) component of the signal. You should subtract the average of the signal to get rid of DC.

Answer 1

[Suneesh]

http://www.mathworks.com/help/dsp/examples/designing-low-pass-fir-filters.html