Hi Matt, why don't you try it out your self, because the terms "slight, major etc." sure are very sujective. Some guys don't notice any difference at all whereas I e.g. always need the highest bitrates and even rather listen to CDs.... Convert one of your favorite songs - copy both versions (MP3, Atrac) to your player and listen to both of them as often as you want to. Then you should be able to notice if the changed quality bothers you.................