Any DJ worth their salt will know that in order to beat-match, or ‘mix’, the tracks they will inevitably have to alter the original pitch of a song to match what’s currently being played. If you don’t do this, the songs will drift apart and your mix will fail.
To prevent this from happening you need to change the speed, or ‘pitch’, of the net song you want to play. Working out how much to slow down or speed up a song by can sometimes be a tedious process; this tool helps.