TO SUM UP: this album is a masterpiece, a work of towering splendour. Mere mortals can only stand at the foot of it and gaze up in wonder at its artistic accomplishment. Yet it is also the poorest selling album of Joni's career.

Taking its cue from the heart-stopping revisit of Both Sides Now on her previous album, across two discs Travelogue pulls 22 songs from her catalogue and has them ambitiously rearranged by big-band com oser Vince Mendoza, recorded with the London Symphony Orchestra and a band including Wayne Shorter, Herbie Hancock and Billy Preston, and re-sung in Joni's life-weathered voice.

Neither jazz, classical, stage nor pop music, Travelogue occupies a unique landscape.

"These are my last two records," she told journalist James Reginato when the album was released, "I'm quitting after this, because the business has made itself so repugnant to me." She stated that, because it was hard to classify, and therefore market, Reprise, her label at the time, "dropped it like a hot potato". It was picked up, ironically, by another Warner Brothers offshoot, Nonesuch.

But the damage to Joni's pride was done and, in the few interviews she gave, she railed against the idiocy of the music business and claimed she no longer fit into it. When your promotional activity reads like a career suicide note, it's no surprise few potential listeners took the trouble to approach. But they missed out on one of pop culture's greatest achievements.

Her voice now with added smoky, oaken tones like a well-aged whiskey, the notes shorter but somehow more eloquent, Joni recasts these disparate songs (not necessarily her best known) as the thoughts of an older, wiser soul. To hear her sing "We've got to get our- selves back to the garden" in the breathtaking new Woodstock, brings up questions of mortality and legacy, and asks if mankind has learnt a single thing about itself since she first sang it. The mature voice may not be as nimble as its forebear, but its acting ability is more acute. Joni uncovers layers of profundity in these songs that maybe even she didn't realise were in there.

She appears to be enjoying herself, able to swing things such as You Dream Flat Tires and Be Cool, both way more engaging than they are on Wild Things Run Fast. Mendoza's charts embrace multiple musics in their scope, and lift this material up to a new place, opening a sky-wide portal to a lifetime of influences and emotion - sweeping classical episodes subside to usher in gorgeous jazz solos - the sound swirling and mutating like a murmuration of calendar pages.

Travelogue will, if you let it, transport you to pop's highest peak.