The ’70s and ’80s private-studio tapes collected on Personal File add up to a truly new way of hearing Johnny Cash. Not only because his voice sounds much more robust than it did on the similarly solo-acoustic American Recordings, but also because this may be the most relaxed Cash on record. That said, he’s fully aware of the microphone; there’s no slacking here. The song selection makes for a kind of musical autobiography, with folk, country and gospel songs he learned as a child sitting next to his own unreleased compositions, and covers of hits by friends and peers. (It can also stand as a version of the celebrated “old weird America” found in Bob Dylan’s work.) Any Cash fan, whether long-term student or curious newcomer, will find this a surprising, mind-opening set.