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Digital editing: How do I best combine two songs into one, basically alternating between the two?

They are in the same time signature, but one is in E major and the other is in d minor. I was guessing that would clash too much (?). I found the change pitch took in Audacity and thought that would be good. Should I change the dminor one to e minor or c? I don't know too much about sound editing. I only have Audacity, but perhaps my university has more I could use. Also, other than fade in/out, are there any other good tricks to use? I want it to sound like a real song, not a poorly chopped together thing.