Here are the two facts you need to know about tonight’s skinny-dip in the boomer nostalgia Jacuzzi: Journey will perform without Steve Perry, and the Doobie Brothers are without Michael McDonald. Those two unmistakable, charismatic voices will be sorely missed, because otherwise both of these San Francisco-originated bands are—sshh, don’t tell Dad—pretty awful. Journey’s “Don’t Stop Believin’” has had a surprisingly lengthy and annoyingly inescapable half-life as fodder for TV commercials and blackout-drunk karaoke nights, but the rest of their catalog is soft, stinky cheese. And while the Doobies racked up several ’70s hits before taking the velvet-voiced McDonald on board, they’re all garbage. “Long Train Runnin’” is super-lame white-dude chunka-chunka funk, and “Black Water” has the worst a cappella breakdown this side of Where in the World Is Carmen Sandiego? Tonight’s sole saving grace might be the opening act: While Dave Mason was overshadowed by the myriad talents of his bandmate Steve Winwood, he nevertheless was an integral part of Traffic for their excellent first two albums, responsible for kaleidoscope-psych gems like “Vagabond Virgin” and “Hole in My Shoe.” His folkier 1970 solo debut, Alone Together, isn’t too shabby, either. NED LANNAMANN