The Campbell Brothers were joined by Maria Muldaur for a rousing set at the Skirball Cultural Center for a Thursday night show last month. Muldaur was more roar than whisper and well matched with the Campbell’s scared steel, providing a generous helping of goose bumpy moments on a very balmy night (an instrumental take of Sam Cooke’s “A Change is Gonna Come” just days before the 50th anniversary of the march on Washington, for one). As with any Campbell Brothers show, there was plenty of spirit to go around and the numbers with Muldaur only took it higher. As Phillip Campbell told it, the same players at the Saturday night juke joints were playing in church on Sunday mornings, intertwining blues and gospel. This bill was a testament.