What's the difference between the version of Sound Studio in the Mac App Store and your version of Sound Studio?
Sound Studio in the Mac App Store and Sound Studio bought directly from us are exactly the same software except that Sound Studio in the Mac App Store is subject to regulations set by Apple. For example with Apple security regulations, third-party software may not work with Sound Studio, so this may affect your third-party audio unit plugins.
Saving in the MP3 file format is available in our version of Sound Studio when you download and install the free and open-source LAME MP3 Encoder. Due to licensing issues, Sound Studio in the Mac App Store does not offer MP3-saving.