When he began writing about blues, country, soul, and early rock-and-roll, Peter Guralnick had one simple goal: to convey his own passion for artists such as Muddy Waters, Merle Haggard, Bobby Bland, and Jerry Lee Lewis, and explain why they were so important.

Guralnick accomplished just that with his first two collections of artist profiles: 1971's Feel Like Going Home and 1979's Lost Highway. Now those volumes are available as enhanced digital editions ($9.99 each on iTunes), with audio and video content and a "bonus chapter" each.

"This is not a matter for me of going back to some long-distance foreign land that I hadn't seen in many years," the 70-year-old New Englander says from Nashville, where he teaches at Vanderbilt University in the spring semester. "It was really a matter of revisiting a place I've never left.

"I met Muddy in 1967, and interviewed him in 1970. But my interest in him and my excitement about his music is no less today than it was when I wrote the chapter [in Feel Like Going Home]."

Or, as he puts it in one of the video segments of Lost Highway: "I'd give up all the records . . . all the CDs . . . all the Spotify, just for one more time seeing Howlin' Wolf live."

For Guralnick, who worked on the project with his son Jake (manager of singer Nick Lowe and others) and Memphis music writer Robert Gordon, the e-books offer a way to expand upon the originals without altering their essence.

In the audio segments, for example, you can hear excerpts from his taped interviews: "This is really cool, to hear Muddy Waters' voice, to hear Howlin' Wolf's voice."

The video segments include new conversations with some of the books' subjects, such as rocker Sleepy LaBeef and Roland Janes, the great Sun Records guitarist and producer who died in October.

The bonus chapters for each book reaffirm Guralnick's gift for nailing the artists he loves in lean, no-frills prose free of affectation. For Feel Like Going Home, he offers a new appraisal of Lewis, the piano-pounding hell-raiser who unleashed on the world "Whole Lotta Shakin' Goin' On" and "Great Balls of Fire":

If there was one person who instinctively embodied the aesthetic of Sam Phillips - discoverer of B.B. King, Ike Turner, Howlin' Wolf, Johnny Cash, Carl Perkins, and Charlie Rich - it was Jerry Lee Lewis. What Phillips was looking for was what he called "perfect imperfection" - he was looking for freedom and spontaneity and feel. What he prized most was not just individuality but individuality in the extreme, in which "mistakes" could give rise to inspiration, in which fearless experimentation could take the artist out on a limb from which only the greatest artistic derring-do could get him back. He was looking, in short, for Jerry Lee Lewis.

For Lost Highway, Guralnick resurrects a 1980 profile of Delbert McClinton. It was written just before the great Texas roadhouse rocker scored his one big hit with "Giving It Up for Your Love," and it just missed the deadline for the book, which includes chapters on everyone from Ernest Tubb and Big Joe Turner to Waylon Jennings and Merle Haggard.

As Guralnick says, "If anyone deserved to be in Lost Highway, it was Delbert McClinton." And his description of the singer, who's still going strong, is as true now as it was back then:

Watching Delbert McClinton on stage is like entering somebody's living room. Not that the music is casual or overstuffed - it's hard, uncompromising music, and Delbert presents it bam bam bam without pause or punctuation, directing the band with forceful energetic gestures. . . . And for the audience . . . it's always a little bit like old-home week at Delbert's shows. There's always something reassuringly familiar - rhythm and blues and honky tonk standards mixed in with originals which in their own, amiable, sprung-rhythm, off-center way oddly present a vision just as spare, just as classic, but made fresh at the same time by the wry poetic consciousness of one Delbert McClinton.

The two essays also point up another common thrust of Guralnick's work, which is to convey the artists' own passion for the music.

"With Delbert McClinton," he says, "you're talking about somebody who was cutting across a neighbor's yard as a kid and he heard Big Joe Turner on the radio and he was struck by lightning. This is what the music is about and this is what I'm trying to communicate."

Guralnick went on to write a celebrated two-part biography of Elvis Presley, 1994's Last Train to Memphis and 1999's Careless Love, and he says Elvis felt the same way. He was less interested in being "the King" than in being seen as part of a musical continuum.

"I think Elvis would be thrilled to have his music taken seriously," Guralnick says, "and taking his place in the tradition, which includes Hank Williams, Arthur 'Big Boy' Crudup, Charley Patton, and the Sensational Nightingales.

"I don't think you can find an ethnomusicologist who was more aware of the various traditions than Elvis."

Guralnick is working on enhanced editions of the Elvis books as well as 1986's Sweet Soul Music and his 2005 biography of Sam Cooke, Dream Boogie. He is also finishing up his long-aborning biography of Sam Phillips, which he says will be published in 2015.

"I had intended to write a brief, elegant book," he says of the Phillips tome. "I hope it remains elegant, but it's not going to be brief. I guess for me, like Sam, it's kind of an epic story."