Cave Story Tribute Site Forums

Hi, I'm new here. I had a question about the Cave Story Mp3 soundtrack you can download from the main tribute site. As I listened to a couple of tracks, it occurred to me that some parts just sounded... sour, like a couple of pitches were slightly sharp. I then booted up the game and listened to the exact same tune, and it wasn't like that at all.

Has anyone else ever noticed this, or am I just crazy? And if I'm not, does anyone know why it sounds like that?