title: How to change audio playback speed using Pydub?
body: <p>I am new learner of audio editing libs - <a href="https://github.com/jiaaro/pydub" rel="noreferrer">Pydub</a>. I want to change some audio files' playback speed using Pydub(say .wav/mp3 format files), but I don't know how to make it. The only module I saw that could possibly deal with this problem is <a href="https://github.com/jiaaro/pydub/blob/master/pydub/effects.py#L53" rel="noreferrer">speedup module in effect.py</a>. However, there is no explanation about how I am supposed to call it. </p>
  
  <p>Could anyone kindly explain how to do this task in Pydub? Many thanks!</p>
  
  <p>(A related question: <a href="https://stackoverflow.com/questions/44035217/pydub-how-to-change-frame-rate-without-changing-playback-speed">Pydub - How to change frame rate without changing playback speed</a>, but what I want to do is to change the playback speed without changing the audio quality.)</p>