Program for editing songs?

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Does anybody know a good program I can use to remix/edit some songs? I've been listening to DJ masa's remixes & mashups right now that's why I became quite interested in editing songs. He can actually rip an instrumental from a song and then paste to it an audio from a different song. I know one or two programs like audacity but I think it only does some basic editing on songs. Can somebody recommend me a good program to use?