The Preservation Hall Jazz Band have cemented themselves as the torchbearers of the Big Easy’s entire jazz heritage. It’s no small burden, but the ambassadors represent their city well, laying down festive, old-timey jazz as well as bone-chilling funeral dirges that have taken on newfound gravity since Hurricane Katrina. New Orleans tourists flock to see these guys in droves, but this weekend they’ll be out of luck: The band is spending this weekend playing three shows here in Milwaukee at the MarcusCenter, the second of which is tonight at 8 p.m.