If you're a lazy bastard like me and you've got a scratched-up CD, then there's actually an even easier way to get better sound on it. All you need is:
a scratched up CDa toileta little soap (optional)Just stick it in the toilet and flush, then watch it swirl around. No joke, the flushing cleans it really well, and no, the CD won't go through the hole in the bottom (although there may be some risk of shigella contraction, but if you're as lazy as me this shouldn't be too much of a deterrent). Rinse the CD off if you used soap, then dry the CD with a soft cloth or towel and you're good to go.
I've also heard that if you haven't got any scratch remover handy, toothpaste can also work. I've tried this before and it didn't work, but I'm entirely open to the possibility that I just did it wrong.