title: Having issue in applying bandpass butterworth filter in python
body: <p>Hy. I've implemented this bandpass filter in matlab for the audio signals and it's working as expected. Now, I tried to implement the same thing in Python but it doesn't produced expected results... (It just sort of discard the whole signal).
  Here is the Matlab code:</p>
  
  <pre><code>[f,fs] = audioread('abc.wav');
  n=6; %order
  beginFreq = (300/(fs/2));
  endFreq = (2300/(fs/2));
  [b,a] = butter(n,[beginFreq,endFreq],'bandpass');    
  %filter the signal 
  filtered = filter(b,a,signal);
  </code></pre>
  
  <p>Here is the Python code (using scipy.signal)</p>
  
  <pre><code>[originalSignal, sampleRate] = sf.read('abc.wav')
  lower = (300/(sampleRate/2))
  higher = (2300/(sampleRate/2))
  n=6 #order
  [b, a] = signal.butter(n, [lower, higher], 'bandpass')
  filtered = signal.lfilter(b, a, originalSignal)
  plt.plot(originalSignal, 'b', filtered,'r')
  </code></pre>
  
  <p>Any kind of help would be highly appreciated. Thanks.<a href="https://i.stack.imgur.com/1UBoj.png" rel="nofollow noreferrer">Filter results</a></p>