Martha Wainwright has an impressive, even intimidating, pedigree: daughter of Loudon Wainwright III and Kate McGarrigle, and younger sister of art-pop wunderkind Rufus Wainwright, he of the operatic tenor and dreamy good looks (now that he’s gotten rid of those goofy mutton-chop sideburns). It’s strange, then, to find her playing at Pete’s Candy Store in Brooklyn, a cute and trendy venue, but one where, even with an audience of 30, everyone is obliged to do his or her best impression of a quiet, attentive sardine. Despite her family connections, Wainwright has no record deal, no record (other than a few self-produced EPs), and a surprisingly small following. You could be forgiven for assuming that she must be talentless, but she is actually an extraordinary musician. Just why she doesn’t have a record deal yet is a mystery, but my best guess is that she’s holding out for a sweet deal from a major label, having seen the example of her brother, whose debut on Dreamworks turned him overnight into the darling of every gay man and every music critic in the country (the same audience?).

Not having a record deal certainly hasn’t affected Wainwright’s confidence, as she takes the stage with all the self-possession of someone who grew up performing, bickering with her parents between songs. I had assumed that she would be playing solo, and was surprised to see bassist Brad Albetta, who plays in her band, joining her on stage. A few years ago I heard Suzanne Vega play a concert with acoustic guitar and electric bass, and while Vega was her usual combination of wit and charm mixed with a healthy dose of blandness, the show did nothing to sell me on the merits of this particular combination of instruments. On this night, it turns out that the crime was not premeditated, as Wainwright informed us that Albetta had just been dropping her off for the show when she noticed that he had his bass in the car, and convinced him to play. Whatever the case, it didn’t make much of a difference: Wainwright is a decent guitarist, but no more, and she has distressingly little sense of how to get a good tone out of her guitar, which often becomes a clattering, ungainly mess in her hands.

Just to be very clear, I’m not in the habit of forgiving mediocre guitar playing because of great singing, anymore than I can enjoy bad singing accompanied by good guitar playing. But you have to hear Martha Wainwright sing to understand just how irrelevant her guitar playing becomes the moment she opens her mouth. This is a magical voice, and it’s impossible to pay attention to anything else that’s going on while you’re hearing it. It is also a very difficult voice to describe, constantly changing timbre and depth, but perhaps you’ll get a sense of it if I say that I can hear in it the hoarse heartbreak of Chan Marshall (a.k.a. Cat Power), the open-throated ecstasy of Björk, the coyness of Rickie Lee Jones, the purity of Joni Mitchell, and, perhaps most of all, the schizophrenia of Canadian cult singer Mary-Margaret O’Hara. Wainwright’s phrasing is consistently inventive, dancing around the beat in a way that Billie Holiday would have admired, and she controls the amount of breathiness in her voice more precisely than any other singer I have heard. Having heard her play a few times recently, I’ve realized with some surprise how carefully rehearsed are all her embellishments and variations on the melody, barely changing from performance to performance. But it doesn’t matter at all, so complete is the sense of spontaneity and playfulness in her singing.

Midway through the set, Wainwright played a few songs from her excellent four-song Factory EP. “Factory” is perhaps her best composition to date, a serene and surreal song, reminiscent of Mazzy Star at their best. Wainwright is not, at least yet, as good a songwriter as her brother, who is perhaps the best young songwriter working today. Her melodies are often catchier than his, but her lyrics often leave much to be desired, especially in her most recently written songs, which veer towards the confessional, with mixed results. Her new songs are so filled with bitterness, with lines like “she’s getting a degree in fucking you,” that, at the risk of turning this review into an unsubstantiated scandal sheet, I’m going to hazard a guess that Martha had an ugly breakup recently. To be fair, though, even her worst songs have flashes of lyrical brilliance, and I don’t doubt that she will develop into an excellent songwriter. But it’s always going to be that voice that’s going to carry her, that voice that insures she won’t be playing tiny venues like Pete’s Candy Store for much longer. Take it from me: Martha Wainwright is going to be a star.