Go to the Media-Convert website. Click on "Choose File" and select the MP3 you want to convert. Make sure the box next to "Input Format" has "MPEG-1/2 Audio Layer 3 (.mp3)" selected.
Select "Audio Interchange File Format (.aiff)" from the drop-down list next to "Output Format."
Click "OK" and the file will be uploaded to, and then converted by, Media-Convert. You will be given a download link once the process is complete.
Go to the YouConvertIt website. Click on "Select it" and choose the MP3 that you want to convert.
Click on the drop-down list under "Convert To." Select "AIFF" from the list.
Enter a valid email address and click "Convert It."
Check your email for a download link to the file.
Click on the drop-down list next to "Output Format" and select "aiff."
Click on "Convert" and the file will be uploaded and converted. After the process is complete you will be given a link to download the file.
Once the file has been converted, double click your file to play it as an MP3.