Cassandra Wilson, Barbican, London

Cassandra Wilson has been trying for years to become a great jazz singer. She has all the components: a great voice, a sultry look, and real presence. The problem is, some of the albums she has put out, such as Dance to the Drums Again, have been ear-achingly awful, while others - Blue Light Till Dawn, Travelling Miles, and her latest, Belly of the Sun - have illuminated her rich talent.

The trouble is, you never know which Cassandra will show up. At the Barbican, she was more hit than miss, striding on to the stage in perky mood and whipping up a round of applause for her warm-up act, the excellent Cleveland Watkiss.

With the backslapping over with, she got down to business. After only a few bars into "Children of the Night", she kicked off her sandals, cracked a broad smile, flicked her golden dreadlocks out of her face and brushed smooth her gold outfit, closed her eyes, and we got the full throaty, smooth-as-molasses blast of that Wilson voice.

The urge was to slide into a cosy chair, grab a glass of red, and let an evening of intimate, smoky red-light jazz flow over you... But wait! We're in the Barbican, a cavernous emporium more suited to a big band blowing the roof off. Wilson doesn't do that. She belongs in a small venue, not an acoustically perfect aircraft hangar. This was even more obvious when she struck up conversation with the audience. The response? Silence. Oh well, Cassandra, better get on with the singing.

This she did, borrowing heavily from Dinah Washington's songbook before slipping into "Last Train to Clarksville", an upbeat rendition that shook the too-polite-to-party crowd out of its stupor, probably only because the song is so recognisable and its delivery was true to the Monkees original.

Wilson then turned up the diva quotient, using blues phrasing and subtly changing tempos to great effect on "Drunk as Scooter Brown". But she stood to one side to let Grégoire Maret on harmonica, then the dextrous Jeff Haynes on percussion, take centre stage.

That certainly got the juices going. A few idiosyncratic jigs around the stage and teasing call-and-response exchanges with her guitarist Brandon Ross seemed to give her the confidence to try a couple of songs that "I only wrote this morning".

It was then time for more of the standard Wilson repertoire: sparse instrumentation and vocal dexterity that eased the best from songs penned by others, notably Van Morrison's "Tupelo Honey" and Bob Dylan's "Lay, Lady, Lay". It all harked back to the days when Wilson first arrived in New York from Mississippi and busked on the subway singing Joni Mitchell songs.

That was in the early Eighties. Now she doesn't need to sing for her supper, but you can't help thinking that that bluesy, startling down-deep bass of a voice should only be heard by a roomful of people at a time.