Last week I made a small remix over my iPhone with Garage Band and when I transferred song to my PC, I found that Garage Band made an M4A format of the song which was not playable on every media player and device. But I found a real simple solution to the problem over the web.
Converting M4A to MP3 – How to
Just go to SoundCloud.com and make an account if you don’t have or you can use your Facebook account.
Then just upload the M4A file of your song.
After you are done you will be able to download the song which will be an MP3 version with almost same quality.