title: Shape of librosa.feature.melspectrogram
body: <p>I'm trying to understand the output of <code>librosa.feature.melspectrogram</code>:</p>
  <pre><code>&gt;&gt;&gt; import numpy as np
  &gt;&gt;&gt; from librosa.feature import melspectrogram
  &gt;&gt;&gt;
  &gt;&gt;&gt;
  &gt;&gt;&gt; melspectrogram(np.random.randn(128), n_mels=128).shape
  (128, 1)
  &gt;&gt;&gt; melspectrogram(np.random.randn(900), n_mels=128).shape
  (128, 2)
  &gt;&gt;&gt; melspectrogram(np.random.randn(500), n_mels=128).shape
  (128, 1)
  &gt;&gt;&gt; melspectrogram(np.random.randn(512), n_mels=128).shape
  (128, 2)
  &gt;&gt;&gt; melspectrogram(np.random.randn(511), n_mels=128).shape
  (128, 1)
  &gt;&gt;&gt; melspectrogram(np.random.randn(1023), n_mels=128).shape
  (128, 2)
  &gt;&gt;&gt; melspectrogram(np.random.randn(1024), n_mels=128).shape
  (128, 3)
  &gt;&gt;&gt; melspectrogram(np.random.randn(2055), n_mels=128).shape
  (128, 5)
  &gt;&gt;&gt; melspectrogram(np.random.randn(2047), n_mels=128).shape
  (128, 4)
  </code></pre>
  <p>What determines the second value of its shape? The first one is clear, it's <code>n_mels</code>, but from the <a href="http://man.hubwiz.com/docset/LibROSA.docset/Contents/Resources/Documents/generated/librosa.feature.melspectrogram.html" rel="nofollow noreferrer">docs</a> I can't understand where the second one comes from.</p>