a bitcrusher should put you on the right track towards that. Toneboosters Time Machine is fairly decent and free. Otherwise yeah try HP and LP filters and distortions (I'd possibly even try a tubescreamer emulator for the distortion)
It's mostly high pass. Metalcore bands love this effect, thanks to Adam D. It's supposed to simulate a bullhorn; the high pass simulates the poor low-end response of the smaller speakers.