For an artist whose music is as beautifully mysterious as Sarah McLachlan’s (at the risk of sounding hackneyed, McLachlan’s hit “Building a Mystery” could itself be a fitting descriptor of her ethereal, otherworldly expression), it’s a wonder that McLachlan foregoes the need to be, in and of herself, a mystery to her fans. With multiple live albums and now a second volume of rarities and B-sides, McLachlan does an admirable job of inviting her audience into her world, giving them full access to the scope and breadth of her work. McLachlan seems unafraid to let listeners hear songs that were deemed unworthy of inclusion on her albums or were released outside her sphere of control, on a soundtrack or another artist’s project.

On the first Rarities, B-Sides and Other Stuff collection, released in 1996, McLachlan could claim a certain amount of ownership over the material. The 13 cuts on that collection included nine which bore McLachlan’s signature, as writer or co-writer. Such is not the case this time around. There are just three original McLachlan tunes among 14 here (one is her arrangement of the traditional “Prayer of St. Francis”). This project feels more like a McLachlan covers album. She interprets the material of a variety of songsmiths, including Lennon/McCartney, Joni Mitchell, Dave Stewart and Randy Newman.

The unique nature of this record bears witness to two truths about McLachlan. First, she is an inimitable vocal talent able to bring her ability to bear on others’ material, skillfully interpreting words and melodies in virtually any context. The second, unfortunately, is that while she is more than able to infuse others’ songs with her style, she sounds most at home on her material, where she has the creative control to craft the soundscapes and textures which best give shape and being to her artistic voice. With no discernable thread or theme to this album, other than culling recordings which have occurred since the last B-sides project, it lacks the unity and focus McLachlan normally brings to her work.

With regards to cover songs, the mark of a gifted artist is their ability to re-contextualize a tune so that it retains the creative spark of its author while somehow simultaneously sounding like a natural piece of the recording artist’s catalog, an extension of their musical vision. There are several cuts here which feel like vintage McLachlan. They provide the most enjoyable and comforting moments on the record. These include a glorious take on Mitchell’s classic “River” which first appeared on McLachlan’s 2006 holiday record Wintersong . McLachlan sounds as if she was born to record this song. Her take on the Beatles’ “Blackbird”, from the I Am Sam soundtrack, and her duet with Bryan Adams on “Don’t Let Go”, penned by Adams and several other writers, sound as if they could have fit within the borders of a “normal” McLachlan record. Her arrangement of “Prayer of St. Francis” is also a glorious and sweetly reverent moment.

Other songs seem like such a departure that they are distracting and ultimately dissatisfying. McLachlan’s lending of her vocals to the DMC/“Cat’s in the Cradle” mashup was an unfortunate choice of collaborations. The idea probably sounded great in the brainstorming stage, but proves to be rather over-the-top. McLachlan’s attempt to re-interpret “Unchained Melody” and turn it into a subtler, more restrained tune denies the grandeur and greatness of the song’s original melody. “Homeless,” which teams McLachlan with Ladysmith Black Mambazo to give fresh life to their Graceland pairing with Paul Simon, works overall, but McLachlan’s contribution is lost in the mix, buried beneath the weight of the other vocalists.

Beyond the good and the bad, there are a few curious choices which are fine, quality-wise, but just seem strange. McLachlan’s take on “The Rainbow Connection” as well as soundtrack cuts like “Ordinary Miracle” and “When She Loved Me” are a bit too poppy for an artist who has made a career of taking pop/rock structures and adding gorgeous, unique layers to them. If McLachlan truly has built a career by building a mystery, those tunes are just too de-mystifying to serve McLachlan well.

This collection is not only a testament to McLachlan’s work with other songwriters but also a chronicle of her ability to surround herself with other great performers. Live cuts featuring Emmylou Harris, Cyndi Lauper and the Perishers appear. While the live mixes do not always flatter the collaborating vocalists, in the way a studio session would, these recordings display both McLachlan’s taste and ability to draw other artists into her creative world.

Rarities, B-Sides, and Other Stuff Volume 2 is not the record to win over legions of new McLachlan fans. Nor was it intended to. This is an album for the serious McLachlan fan who wants a hard copy of that tune they’ve heard floating around the Internet or saw in a rare, wonderful live setting. The project does just enough to add to McLachlan’s allure without detracting from the legacy she continues to construct.

• Various Songs MySpace