It's because mp3 dramatically changes phase. As a result, merely mixing the inverted original won't leave you with what's filtered out. That technique will wor

It's because mp3 dramatically changes phase. As a result, merely mixing the inverted original won't leave you with what's filtered out. That technique will work with simpler compression techniques, like companding. (Companding is basically doing the digital equivalent of the old Dolby NR button from the cassette days.)