“We have had a few technical problems,” says guitarist Richard Knox, explaining the reason for the late start in Glissando’s set. “Our keyboard’s fucked.”

Knox and his band mate in Glissando, vocalist and keyboardist Elly May Irving, have spent the last twenty minutes on and off and then back on the stage trying to get Irving’s failing instrument to start up. They have finally conceded defeat and had to resort to borrowing support act the Field Mice’s synthesiser, a monolith of a Roland in comparison to Irving’s stubby Casio.

“It is like something out of Star Wars,” quips the dryly comic Knox about it. Knox and Irving are in the middle of a ten date UK tour, their first in two years as a duo, and without the Fleeting Glimpse Ensemble, a rotating line-up of approximately twenty other musicians, anything between one and half a dozen or so of them who usually accompany them for gigs.

Edinburgh has long been a stopping-place for the Leeds-based ambient/post-rock band, and much of the forty-strong crowd is made up of friends which Knox and Irving have made at other Scottish gigs. These include Conquering Animal Sound, another Edinburgh-based post-rock two-piece, who have recently signed to Knox’s record label Gizeh Records and who will be releasing their debut album there in the autumn.

Richard Knox and Elly May Irving were once an item. They lived together at the time they formed Glissando at the start of the last decade, but broke up in 2007. While they have remained close friends, the collapse of their romantic relationship gave them the spurt they needed, after years of largely unsuccessful attempts at recording in their home studio, to finish their 2008 debut album, ‘With Our Arms Wide Open We March Towards the Burning Sea’.

A sense of looming potential chaos, that everything might collapse at any moment into complete disarray extends also into Glissando’s performance.

There is no set list. Knox and Irving spend a lot of time debating back and forth with each other between numbers about what they should play next. One song starts up, falters to a stop as they miss a cue with one another and has to be started up again. Irving, cohered into it by Knox, is about to play a Tom Waits cover, but this has to be abandoned when they realise that they are nearing the venue’s curfew. They finish instead with ‘Floods’, one of the stand-out tracks from ‘With Our Arms Wide Open...’

Yet all this far from deflating their performance in many ways makes it. It has not been a good night for Glissando. When they do get down to the business of performing they are, however, simply spellbinding.

Knox, fiddling occasionally with his amp and effects pedals, during two of the songs in the five song set gliding a bow across his instrument, is a methodical, steady guitarist and the solid backbone of the duo. Irving meanwhile is extraordinary. As her hands breeze surprisingly gamely across the keys and unknown terrain of the Field Mice’s synthesiser, her ethereal vocals imply a great sense of sorrow and loss. On songs like new single ‘The Long Lost’, and across album tracks, like ‘With a Kiss and a Tear’ and ‘Floods’ for all their pain, there is also, however, a fragile feeling of hope and a sense of astonishment at anything having survived at all. What Glissando do is make music that is not only haunting but also holistic.

Tonight’s show has been chaotic, scrambled and in many ways something of a mess, but also, like Glissando themselves, has had its own sense of totally fitting and stark, against-all-odds beauty.