They are the same, and can be used interchangeably., but with a slight difference of emphasis: 'before' focuses attention on the past, 'already' focuses on the present. These differences are more important in constructions/contexts where the choice is more obvious: Shall I play the song for you now? No thanks, I've already heard it. i.e. I am a person who has head this song. What's that melody? I'm sure I have heard it before. i.e. I am trying to remember something in the past.