The Unthanks: Mount the Air (Cadiz Music)

Quietly and steadily, Northern folk-singing siblings Rachel and Becky Unthank have carved an impressive niche for their eponymous band. Praise flowed for albums Last and The Bairns, the latter nominated for the Mercury Prize and BBC Radio 2's Best Folk Album in 2008 - while Rachel Unthank's Cruel Sister album with the Winterset scooped MOJO's Folk Album of the Year in 2005.

Recent recordings have seen them add a lacing of other genres and intriguing transformative covers like King Crimson's 1970s avant-prog classic 'Starless' or Tom Waits’ 'No One Knows I’m Gone'. All in all, a sense of ambition has been in the air - which seems brilliantly realised with the title track opener on this latest album.

Mount The Air is magnificent, a spine-tingling multi-layered 10-minute chamber folk piece with gorgeous jazzy brass inflections through which the sisters' voices flow as if channelling Sufjan Stevens and Efterklang at their best. And ten tracks later, sprightly closing instrumental 'Waiting' bookends proceedings nicely with another dip into a diverse instrumental ragbag that skips through little variations like a fond farewell dance.

In between, however, things go a little awry. Like Last, the album seeks to create an air of mournfully immersive reverie, with little change in tempo and instrumental feel between tracks. And though sometimes the mournful minimalism works, too many tracks fall flat, the twee 'Madam', cringe-making 'Lullaby', mawkish 'Foundling', plodding 'Hawthorn', and 'Died For Love' with its drippy piano and syrupy strings.

Thankfully, there are a few songs worthy of adorning The Unthanks' songbook: the resonant 'For Dad' stands out with its folky drone and skirling wandering soul violin; the eerily menacing 'Magpie' with its dark lyrical borrowing from the nursery rhyme One For Sorrow. 'Flutter' starts promisingly with warm electric keys and quietly declamatory vocals that hint at Bjork but then messes up as strings come in that really should have been left well away.

Less kow-towing to the glum side of a band of self-confessed “miserable buggers” would have been good. As it is, we're left with one masterpiece track, a few good 'uns - and a few too many clunkers.