Bryce Dessner, Nico Muhly & Sufjan Stevens, The Barbican, London

Here's a promising trio: Bryce Dessner, guitarist for The National; classical and pop composer/ arranger Nico Muhly, who has scored films including The Reader as well as operas and ballets, and Sufjan Stevens, the genre-hopping American songwriter.

The three are buddies, and the main attraction of tonight's show is their collaborative 12 song cycle, taking inspiration from the solar system, entitled Planetarium (guess The Planets was already taken.)

First, though, are instrumental pieces composed by each of them, performed by the almost aggressively expressive Navarra String Quartet. What strikes you here is the ambition of these musicians beyond the three-minute rock song. It's not all successful – there's some teeth-grittingly harsh sawing and the odd snoozy movement – but concentration is mostly well rewarded.

But mildly challenging chamber music is not really what the crowd came for. The second half is, however, exactly what you'd expect their collaboration to sound like. There's Steven's vocals, veering between dusty wistfulness and punchy falsetto; seven trombonists to add a brass weight; glitchy tweaks and electronic beats; there's Muhly sitting in the right angle between a piano and a celeste. After the second track, the bombastic 'Jupiter', you can almost feel the relief in the room: to quote their lyrics, “by jove!” - there's actually a graspable tune here.

Each planet, plus the sun and moon, gets its own song, and hanging over the stage is a giant balloon, with varying planet-like projections. It's a cute idea even if it does more resemble a giant saggy peach than a ball of burning gas.

Some numbers achieve heavenly heights. 'Pluto' (“the little planet that could”, quips Stevens, “the foster child planet”) demonstrates Dessner's gorgeous guitar playing, chiming out a harp-like arpeggiated figure. 'The Earth' builds in a satisfying way, its strings and simple vocals raised up by all those trombones, with more of Dessner's guitar swooping lushly.

The concerts notes explain the planets are just metaphorical jumping off points – this isn't Holst-like musical portraiture – yet where Planetarium bizarrely struggles is for variation, and definition. Several tracks sprawl into a proggy, predictable slush, drowned in brass (seven trombones ain't exactly subtle). And the lyric tone is almost uniformly melancholic, even if the vocals sometimes sound silly: Stevens is still much enamoured of the vocoder, alas, and this Auto-Tuning turns his naturally splendid voice into a naff horror. The vocoder needs to be sent far away from him: outer space would do nicely.