It was a rare opportunity: a chance to experience Olivier Messiaen’s Harawi , a song-cycle rarely-performed on account of its considerable demands on singer and pianist: most would consider very carefully before taking it on. Inspired by Wagner’s version of the Tristan and Isolde legend and its Love-Death (Liebestod) ending, it is the first of a trilogy. The performance I saw was on the Saturday morning of Leeds Lieder+, the fourth biennial festival of art-song from around the world, directed this year by pianist Malcolm Martineau. Mezzo-soprano Hetna Regitze Bruun and pianist Kristoffer Nyholm Hyldig, both Danes, presented us with a Harawi which was difficult to fault, one which has been well matured after several years in the Bruun Hyldig Duo’s repertoire: they have been performing it in Denmark since 2008. Immaculate might be the best description of what I experienced.

In the brief introduction, the composer was described as ‘a poet of nature’. True, but he also had a distinctly scientific side, making recordings of exotic birds on scratchy 78s and rendering them into human music as accurately as possible. Because that music flies differently, to say the least, much precision is demanded. Bruun was alert to all demands, from the subdued La Ville qui dormait, toi , the first song, through ecstasy and terror (which merge) and erotic moments all the way to the final twelfth song, Dans le noir , which brings us into the dateless darkness of eternity. Hyldig was absolutely at home with the birds, super-dextrous and adroitly fluid, stretching arm-muscles, never missing. Bruun has all the flexibility needed, her voice free of most of the tremolo found in the voices of some ‘grand’ singers, but adorned with colours.

The influences on Messiaen from Surrealism and French Catholicism, and his liking for made-up words and Quechua, the language of the ancient peoples of the Andes in South America, make interpretation of his lyrics with their densely-packed images and their religious symbols difficult for most mortals, but the love-death narrative is relatively straightforward, and the two performers take us on a well-beaten track. Bruun was endearingly intimate when she addressed the beloved as a green dove back from Heaven and a limpid pearl – recurring images of nature, peace, preciousness and transparency – and impressively urgent as she delivered lines about darkness, an abyss and vertigo in Montagnes, accompanied by the sound of bells and deep bass plunges from Hyldig at the Steinway. This was a performance to fall into, then soar upwards with.

The equivalent of a show-stopper, if such a thing can exist in Messiaen’s work, was Doundou tchil – onomatopaeic words representing the sounds made by the ankle bells of ceremonial dancers, I imagine in a temple courtyard not far from Machu Picchu as exotic Andean birds swirl around overhead. It is comforting to know that a devout Catholic steeped in the pronouncements of St Thomas Aquinas can be that playful! Bruun was thrilling as she sang lines like “Tongou, tongou, mapa, mama” accompanied by a Hyldig powered by pure adrenaline.

When the ankle bells returned, in the intensely surrealist incantation Répétition Planétaire , which uses plenty of Quechua and pseudo-Quechua, the dark humour became manic before it changed to desperation, as Bruun delivered the required sighs and cries of a sort that might damage vocal cords if done with insufficient restraint, adding a touch of the erotic - “Ahi! Ahi! Ahi! O!” Then came a spiral staircase, a red star and a whirlwind ("Escalier tournant./Tourbillon, étoile rouge, tourbillon” ), the stuff of nightmares, as the tempo became frantic: Hyldig was breathtaking here. By the time Bruun reached the penultimate song, Katchikatchi les étoiles , she had fleshed into the full tragic heroine, singing its final lines – “Tou, ahi! mane, mani,/Roule dans le sang!...Ahi!” with great force, accompanied by a dramatic fling of her arm in a performance which had until then been largely free of bodily gestures. This song was another in a series of triumphs for Hyldig as well, as his playing had to reflect the fact that the lovers are seeing (according to the extensive notes provided by Leeds Lieder+) “the whole micro- and macrocosmos jumping up and down like grasshoppers”. Katchkatchi is Quechua for grasshopper. Hyldig helped me to picture that!

I was particularly moved by the final song, Dans le noir, which contains the line “Mon amour, mon souffle! (My love, my breath!) and I thought of Messiaen composing at a time when his wife was dying of a terminal illness. The lovers are united in death, transformed.

The Bruun Hyldig Duo has appeared mainly in Denmark, and has toured outside the country to some extent, but deserves a lot more international exposure on the evidence of this performance in Leeds.