Malian song duo Amadou & Mariam have been performing Afro-blues, pop and dance just shy of 40 years. Their partners in crime are the Blind Boys of Alabama, a trio who met as children, who they have been performing alongside long before this festival. Together again, you can sense the connection. These are performers who stand above the hacks they have seen rise and fall. Bringing rapturous gospel across the globe, there is no audience they cannot conquer – except for middle-class Edinburgh.

We’re a decade or so past the days where Usher Hall would remove the seating for such an event. Still, you cannot deny gospel royalty nor appreciate its presence, even if this is a wholly new experience for you. As they arrive, The Blind Boys of Alabama, five Golden Globes to their name, open the event with Walk in Jerusalem.

Emotionally charging, this is an elemental force of vocals. All of these men, with a little more rasp to their smoky tones, are the dictionary definition of ‘down to earth’. You will never, no never, be this smooth. Briefly joining them, Amadou & Mariam raise spirits higher, their nature touching. With an impromptu birthday celebration for Alabama Boy Ben, we’re drawn inwards – only to feel disconnection eek inwards.

There’s a definitive sense of reverence on display, as opposed to amazement. There’s a sad sense of two crowds here – those blinded by adoration, and those politely nodding along. Suddenly, without warning, people cheer: there’s a fire blazing inside. Amadou riffs a guitar solo and the duo is ready to inject some Afro-pop into a dreary Scottish evening.

Eruptions can occur when there’s gentle encouragement. It isn’t until Two Cultures, One Beat – a premiere performance of a new collaboration by the two groups – that the audience rise to their feet. This is what we expect. This is what the Blind Boys can conjure. The composition, which celebrates the common language of music, finally raises the roof. There are whoops, dancing in the aisles and the occasional tender embrace by patrons recalling their youthful listenings.

Intrepidly, they carry on. Valiantly so too, though you can’t help but scrunch your face in embarrassment as Mariam has to keep people from sitting. It’s all a little too late, and it’s nothing at the fault of the creatives on stage. Amadou & Mariam, along with the Blind Boys of Alabama try their best to re-ignite a passion, but the audience plays too close on the safe side.