ALTAN: "Island Angel" (Green Linnet)

WHEN SMOKEY sings, Martin Fry hears violins. When Mairéad Ní Mhaonaigh sings, I hear grand opera.

Ní Mhaonaigh's voice is a national treasure, but it's one that will never need an interpretative centre. It is an interpretative centre. On Island Angel she sings a song in Irish called 'Dúlamán'. The instant I heard it, I was smitten. Her performance is truly haunting and she imbues every line with a sense of inherent sadness that is as compellingly sweet as it is heartrending. Surely, I thought, this must be one of the great traditional ballads of loss and longing.

Then, I read the sleeve notes. 'Dúlamán is actually a nonsense nursery rhyme about seaweed. Seaweed! Christ, this woman could sing The Satanic Verses to the Ayatollah Khomeini and have him begging for more.

All Altan albums come complete with P45s for music critics. Beyond an enthusiastic endorsement, reviews of what they do are redundant. How can you possibly even begin to describe that split second in a set of Altan reels when the twin fiddles of Ní Mhaonaigh and Ciaran Tourish merge in the fast lane with Frankie Kennedy's incendiary flute? Similarly, I defy anyone to paint a word picture of what Mairéad's vocal chords can do to a song without sounding like a babbling fool who's just swallowed either a Roget's Thesaurus or a bottle of Paddy. Or both.

What I can tell you, however, is that Island Angel is Altan's finest collection thus far. The instrumentals are an especially exotic bunch. There are jigs, reels, highlands, a strathsprey and a mazurka, which is a dance tune from Poland with more than a hint of Gaoth Dobhair in its veins. The enlistment of accordionist extraordinaire (not to mention Sharon Shannon's main squeeze), Dermot Byrne, adds some welcome extra ballast to the ensemble playing that will probably be even more effective in live settings.

Ultimately though, it's the songs that do it for me. There are five here, each one of them a mini epic of passion, poignancy and other, more indefinable qualities. Indeed, with both 'Bríd Og Ní Mhaile' and the aforementioned 'Dúlamán, Mairéad Ní Mhaonaigh has undoubtedly recorded her best vocal performances to date. And that really is saying something.

Every Altan album is essential. Island Angel is a downright necessity.

• Liam Fay