Johnny Cash's musical journey through the heart of America began 50 years ago. And though the Man in Black has turned gray — he celebrated his 70th birthday this year and has been in ill health — the country legend is still going strong musically.

A new CD, The Man Comes Around, finds Cash singing his own songs as well as those of other artists ranging from the Beatles to Trent Reznor (Nine Inch Nails). It's Cash's fourth record with hop/metal producer Rick Rubin, with whom Cash began to collaborate in 1994.

"If the songs are really great, if the writer is good, if the song is really there, if I like it, if I feel like I can do it and make it my song and enjoy it myself, then it's going to be mine," Cash tells Morning Edition host Bob Edwards in an interview at the cabin he uses for a recording studio on his property in Tennessee.

Cash recalls the first songs he did for Sam Phillips' Sun Records in the 1950s, backed by Luther Perkins and Marshall Grant — two mechanics he met in Memphis.

"We started going to each other's house at night and playing music just for the fun of it. And at one point, we were invited to play at a church... And it felt good, so we said, 'Let's do some more shows.'" They would play at movie theaters and other locales around Memphis and the mid-South, Cash says.

He also explains the band's distinctive rhythm that came to be known as his signature sound — a train moving down the line. It was the combination of Perkins laying the heel of his hand on the strings on his Fender Telecaster and Grant pounding his upright slap bass with "the snare drum side effect," Cash says.

The result was a unique blend of musical genres. As Edwards reports: "The first big hit, 'I Walk the Line,' established Cash as a performer who didn't quite fit the mold of traditional country or the new crowd, the rock 'n' rollers. Folk, maybe — or perhaps a category uniquely his own, called Cash."

Cash admits he's hard to categorize, musically and politically. "Maybe it is a conscious thing to be all over the place," he says. "A person of my position and situation is in a position of responsibility, for one thing, to answer the call for those who need a voice. I'm not saying that I'm the nobleman to jump up and rally to the call, but sometimes I can remember to."

His famous recordings in — and about — prisons added to the Cash mystique. In 1968, Cash actually recorded a live version of his 1955 song "Folsom Prison Blues" at the California prison by that name.

"Well, my whole thing about recording in prisons was because I thought it would make an interesting record. I heard that sound of that audience applauding me in a prison in 1957. And I told my band that day, I said, 'We've got to record a show at a prison and get that audience response on record.'"

In the interview with Edwards, Cash also touches on the religious influences of his music, including "The Man Comes Around," the title track of his new CD, and "Personal Jesus," the 1987 hit by Depeche Mode. "To me it's a very fine, fine evangelical song, although I don't think that's why it was written," Cash says. "It's where do you find your comfort, your counsel, your shoulder to lean on, your hand to hold to, your personal Jesus."

As for the variety of artists he has covered, Cash says with a laugh: "Nobody's safe."

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