I get a lot of the crack from the bottom snare mic. I usually boost a lot around 5k and 200. It will sound weird when played by itself but great in the mix as long as you have it a little lower than your top snare mic. If you don't have good seperation on your kit though, you may need to gate it pretty hard since this is only to get a crack in the snare and will hurt the sound of your toms usually if they are picked up a lot in the bottom mic. I usually compress the bottom snare mic a little harder than the top too.