While we recognize that you are likely listening on a 'fidelity-challenged' system (eg. computer) we think you will be able to get a rough idea of what kind of difference mastering CAN make to your project by listening to these before and after examples. These are MP-3 files encoded at 192 Kbps.
Mastering Christina Jade - "Breathe" Before Download MP3 After Download MP3
Restoration Leon Gold - "Havdalah" Before Download MP3 After Download MP3