I'm looking for a service (preferably free) which will cleanly isolate audio when I have a separate audio file that has everything I want to remove. More specifically: I have audio of someone talking and a song in the background. I also have audio of just the song. I'm looking for a program that will give me just the person talking.

I found vocalremover.org which usually works really well but it (understandably) fails when the song also has vocals. I also tried doing it manually with audacity but the result was kind of scuffed.

Any help appreciated.