In case you're unfamiliar, Extortion is some nice, cozy, soothing, heavy hardcore band from Perth, in Western Australia. You might like them, you might not. Personally, I don't think that they're anything super special; I've heard a shitload of bands that sound exactly the same.

Septic Surge is a really lo-fi noisy-ish powerviolence band with a lot of grind vocals. Again, also from Australia. Again, nothing too special. They sound like a lot of early powerviolence bands, i.e. Man Is The Bastard, Crossed Out, etc. A lot of their recordings sound really fucking blown out.