Part of the (included with BB/RB) DXi plugin called PGDynamics is the Expander/Gate.
Just as a compressor 'compresses' the levels, the Expander expands them. PGDynamics plugin includes both.

To try to explain this; using an Expander the lower volume sounds are made even lower, and higher volume sounds are made louder.
They add 'Gate' to the name because, if set just right, you can virtually eliminate lower level sound.

The more you know!

I do not work here, but the benefits are still awesome
Make your sound your own!