In this tutorial, Dan Worrall explains the concept of upward compression, and shows various useful applications on full mixes, drums and guitar, using FabFilter's Pro-MB multiband compressor/expander.
FabFilter Pro-MB is available via http://www.fabfilter.com/shop . For more information, see http://www.fabfilter.com/products/pro-mb-multiband-compressor-plug-in