Subtracting extra audio?

[DemonSpawn]

I'm trying to figure out a way to remove unwanted sounds from an audio stream.

Now, from physics theory it seems easy enough. Get the exact audio that you want to get rid of, reverse the amplitude of the waves, and add the streams together, getting rid of that one sound. Of course, I have no idea how to do this, or if will even work properly.

Does anyone have any experience in this sort of thing, or have an idea where I can start?