Fidelizer will instantly turn your Windows Vista/7 computer to audiophile workstation for sophisticated audiophile player like J River, XXHighEnd, HQPlayer, foobar, etc. It involves no permanent modifications so system will remain safe and sound after restart so even system with normal Windows installation can experience better sound quality when needed. Backgrounds behind the optimizations is far advanced for someone daring to make free software so grab it while it lasts. Fidelizer has 3 optimization levels. They're all for the same goal to sonic improvements. I'll leave them all to your judge whether they're subtle or big difference. At any rate, you should leave your ears with it for at least week if it doesn't hurt your computer. Some people need time to adapt to changes.