Audacity is good, but a DAW with non-destructive editing is definitely the best thing you could ever get for yourself. I don't think you're gonna find a free DAW with that feature though...
Brocas Helm/Hatchet/Exmortus/Midnight Chaser 11/22
High on Fire/Kvelertak 12/12
Exodus/Nails/Hellfire (???) 12/20
Neurosis/Bl'ast!/YOB (???) 12/29