title: Calculating power-spectrogram on a window of a .wav file
body: <p>I am trying to calculate the power-spectrogram of a part of a soundfile.
  Currently I am using <a href="http://bmcfee.github.io/librosa/" rel="nofollow">librosa</a> for this.</p>
  
  <p>I am calculating my windowsize by 20*1e-3*samplerate. 
  What I am wondering about is the result (specifically the length of t) as can be seen in the example below:</p>
  
  <p>A samplerate of 44.1kHz combined with the timeframe of 20ms yields a window of 882 samples.</p>
  
  <pre><code>In [2]: D = np.abs(librosa.stft(y[:882]))**2
  
  In [3]: np.shape(D)
  Out[4]: (1025, 2)
  </code></pre>
  
  <p>What I get is a 2ms timeframe in my result, which is not what I expected. Can somebody help me / point out what I am doing wrong?</p>