You can use Apple ITunes to convert to AAC. After you dl it, go to edit, preferences, click on the importing tab, and use AAC encoder. Then load the song you want to convert right click on it, and go to conveert to AAC. Now, you will lose sound quality. I am very new to this, so this might not be the best way, to convert for the reason you want to do it, but I know this way works...
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