Joanna Newsom, Barbican, London <!-- none onestar twostar threestar fourstar -->

As she walks on stage, dressed head to toe in black, with hair cascading down to her waist, Joanna Newsom looks just like another member of the orchestra.

The crowd erupt into worshipful applause, followed by hushed reverence. Even her shoes - five inches tall, vaguely S&M - mean the business. From the opening song "Emily" - her tribute to her astrophysicist sister ("You taught me the names of the stars overhead, that I wrote down in my ledger") - it's immediately apparent that Newsom has come of age. A girlish brightness remains in her voice but without the squeakiness of a few years ago.

And so she plays Ys in its entirety, backed by the celestial strings of the LSO. Newsom is a still performer, her small frame encumbered by a huge harp, but her music has a movement and life of its own.

"Monkey & Bear" crescendos into a swirl of strings, tribal drums and chanting. When the orchestra quietens, her virtuosity is only more apparent. Alone with her harp, "Sawdust and Diamonds" shimmers impossibly. The effect on the audience is almost paralysing. Not a single person moves, speaks or even twitches.

After a short interval, the atmosphere loosens. The London Symphony Orchestra have been banished into the wings, and the whimsical Newsom of old seems to make a return, wearing a puff-sleeved dress and skeleton-print leggings. And - gasp! - she speaks. "This isn't a Christina Aguilera-style costume change," she tells us. "I was just sweating really hard." The audience laughs like she's told the greatest joke of the century.

And when the staccato opening bars of "The Book of Right-On" from The Milk-Eyed Mender sound across the venue, the first whoops of recognition follow (naturally, Ys is far too conceptual and serious for whooping). And she shows herself to be a great interpreter, too, with a lovely rendition of Scottish folk song "Ca' the Yowes to the Knowes". For her encore, Newsom sings "Sadie"; a spotlight shines on the singer, her golden hair, her golden harp and her golden voice.

Lately, male critics have become rather fond of lumping her in with Kate Bush and Björk - heart-pounding genius boiled down to female kookiness - but it does none of these unique and wonderful artists any favours. At the Barbican, it became clear that Newsom is very much her own woman.