title: Convert multi-channel PyAudio into NumPy array
body: <p>All the examples I can find are mono, with <code>CHANNELS = 1</code>.  How do you read stereo or multichannel input using the callback method in PyAudio and convert it into a 2D NumPy array or multiple 1D arrays?</p>
  
  <p>For mono input, something like this works:</p>
  
  <pre><code>def callback(in_data, frame_count, time_info, status):
      global result
      global result_waiting
  
      if in_data:
          result = np.fromstring(in_data, dtype=np.float32)
          result_waiting = True
      else:
          print('no input')
  
      return None, pyaudio.paContinue
  
  stream = p.open(format=pyaudio.paFloat32,
                  channels=1,
                  rate=fs,
                  output=False,
                  input=True,
                  frames_per_buffer=fs,
                  stream_callback=callback)
  </code></pre>
  
  <p>But does not work for stereo input, the <code>result</code> array is twice as long, so I assume the channels are interleaved or something, but I can't find documentation for this.</p>