Noxon metal polish is very fine grit liquid and will help restore to playability lightly scratched discs that are troublemakers. I use clean toilet paper the cheap kind with no perfume in it---just nice clean paper. That and some Noxon does the trick for most CDs that are becoming unplayable due to too many error corrections and scratches. Mequires makes a real useful hand polishing kit for plastic headlights. It saved my 20 year old BMW headlights by removing the years of abrasion with sandpaper and then polishing the plastic to like new status. Some CDs won't play reliably with truly deep scratches. I use the Mequires on those as a last ditc h effort to revive them. So in my experience if a simple surface scratch is messing up the fidelity you can polish away and get it back to playable without much difficulty.