Changing playback speed requires intensive real-time calculations. Depending on the complexity and quality of the audio file, the effect of the time-shifted audio will vary. Drum tracks, for example, may have a slap-back (echo) effect when using the speed function. Another factor is how far the audio is time-shifted from its original speed--with better quality results occurring the less an audio file's speed is shifted. Keep these considerations in mind to achieve the best results when changing an audio file's playback speed.