Once upon a time, in a record business far, far away, musicians were free to dip into whatever genres they pleased without much fear of commercial catastrophe. Those days, which now seem like a golden era of autonomy, are glowingly recalled on Classic Live! (DIG), a collection of newly unearthed mid-'70s concert tapes by Maria Muldaur. Best known for her seductive 1973 chart-topper ''Midnight at the Oasis,'' Muldaur was more than a one-sexy-hit wonder. The original jam-band hippie queen applied her lithe, sassy-waitress voice to everything from jug-band music to jazz, gospel, and blues. As this album proves, Muldaur was as convincing sweetly warbling Dolly Parton's ''My Tennessee Mountain Home'' as she was losing herself in the Billie Holiday-associated ''Lover Man (Oh, Where Can You Be).'' And thanks to supple backing by the likes of legendary jazz drummer Earl Palmer, Classic Live! is the friskiest musicology class you'll ever attend.