It has been four years since Emmylou Harris' last studio album, but patient fans will be rewarded in the coming months with two new releases, Billboard.com can reveal.

First up is an 80-song boxed set due Sept. 18 via Rhino, which features two discs of off-the-beaten-path studio work and two additional CDs of rarities, many of them previously unreleased.

"For the most part, none of these songs have ever been on a compilation before," Harris tells Billboard.com. "They're kind of favorites -- I call them my orphans, songs that maybe I didn't even perform that much but I loved enough to record in the studio. They didn't quite fit either the Hot Band or whatever I was doing. Things like 'Coat of Many Colors,' which was one of my favorite songs of all time, or 'Ballad of a Runaway Horse' and '1917.'"

Also included are several unreleased recordings with her Trio, which also featured Dolly Parton and Linda Ronstadt. "There's an outtake from the aborted Trio album that we did in 1978, a Carter Family song called 'Palms of Victory' that's just live off the floor," Harris says. "There's not even a solo on it -- it's just the band and the three women singing and I sound like I'm channeling Sara Carter. I wish -- in my dreams!"

The second two discs boast numerous tracks Harris has recorded for tribute albums to such acts as Gram Parsons, Merle Haggard and Townes Van Zandt, as well as the original demo for "All I Left Behind" with Kate and Anna McGarrigle.

Harris put her next studio effort on hold to finish the boxed set, but is making progress on a new Nonesuch album with assistance from the McGarrigle sisters and Seldom Scene lead singer John Starling. Harris duets with the latter on "Old Five and Dimers" ("I finally decided that I was old enough to cut that song, reaching the grand ole age of 60," she laughs).

"It's kind of a combination of some of my own songs, some songs that I've wanted to record for a long time and some new things that I came across," she offers of the effort. "You'll get obth Emmylou the interpreter and Emmylou the songwriter."

Harris, who will also tour heavily into the fall, has recently recorded guest spots for Parton's next studio album, an Anne Murray duets album and old friend Danny Flowers' "Tools for the Soul."