Lets say you have an normal song with two layers, one instrumental and another of just vocals. Now lets say you also have just the instrumental layer. Is it possible to "subtract" the instrumentals and obtain the pure vocals? Is there going to be loss? How would I go about performing this specific type of subtractive synthesis?
Using a technique (and software) like this: Audacity Vocal Removals I bet you can achieve what you need. As Daniel and Paolo said if you can apply the inverse of a soundwave to the original soundwave you are able to cancel it out (muting the sound).