title: butterworth filter for signal processing
body: <p>I have a school project to be able to move a wheelchair according to user instruction. I am currently starting my project by using matlab and have acquire several data for the training purpose. I am stuck at applying the butterworth filter to the signal,</p>
  
  <p>this a sample of my training data 'go' <a href="https://drive.google.com/file/d/0B4Y0BvHzLaILaUpqeFpjWFV3eFE/view?usp=sharing/" rel="nofollow noreferrer">link</a></p>
  
  <p>here is my code</p>
  
  <pre><code>[x,Fs] = audioread('go10.wav'); % to read the data
  
  plot(x) ; % plot the data before aprplying the filter
  
  n = 3; % the number of order
  
  beginFreq = 800 / (Fs/2);
  endFreq = 2000 / (Fs/2);
  [b,a] = butter(n, [beginFreq, endFreq], 'bandpass');
  
  y = filter(b, a, x);
  
  figure;
  plot(y) ; % plot the data after applying the filter
  
  p = audioplayer(y,Fs);
  play(p) ; % play the record after applying the filter
  </code></pre>
  
  <p>here the plotting result,
  <a href="https://i.stack.imgur.com/mqOVN.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mqOVN.jpg" alt="this is the signal after the filter"></a></p>
  
  <p>So my question is, </p>
  
  <p>1) Did I do it right? about the begin and end frequency? and does my n correct?</p>
  
  <p>2) And what can you tell me about this butterworth filter? I know that it trying to focus on the human voice, but what exactly it does?</p>