Scratch can import uncompressed WAV files and some MP3 files. Sorry but I don't know which MP3 files work and which ones don't. I suggest converting to WAV using the free Audacity audio editor if you have trouble.
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Here's an unknown fact...
(1)Open iTunes.
(2)Click the song you want.
(3)Go to Advanced>Create AAC Version.
(4)DONE!
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