He will be conducting the Berlin Philharmonic and the chorus, flown over for the occasion, will be provided by the Atlanta Symphony Orchestra, where Runnicles is winding down his long-running principal guest conductorship.

As the combined forces rehearse for the massive Requiem in Berlin’s fabled concert hall, the Philharmonie, there will be another figure in the auditorium. She might well be alone, but, as the rehearsals progress, Runnicles will refer repeatedly to her, sit down with her to seek her comments on vital points of balance as perceived from off the front of the stage, and take her advice on the ever-critical issue of balance between the orchestra and the chorus.

Runnicles describes her as his “extra ears” in the hall. Her name is Jessica Cottis. She is a young Glasgow-based conductor, aged 29, and graduated from college only four months ago. By any standards that would be a remarkable achievement and opportunity: four months out of school and you’re off to Germany to work at the Berlin Phil. But Cottis, a cool, contained, super-articulate and engaging young Australian-born musician, is already racking up significant achievements.

She has a fellowship in conducting at the Royal Scottish Academy of Music and Drama, where her post slots neatly into the brand new collaborative partnership between the academy and the BBC SSO. And part of that entails her being assistant to BBC SSO conductors, including Runnicles; ergo the Berlin connection.

But she holds another fellowship at her alma mater, the Royal Academy of Music in London, where she studied conducting and is now Manson Fellow in Conducting.

We don’t really know her up here yet, though there was a brief glimpse of her conducting in the recent Red Note ensemble concert given in conjunction with the Peter Maxwell Davies 75th birthday celebrations.

She has been booked to conduct Red Note’s upcoming Tune Up tour of Scotland in the spring, which will feature William Sweeney’s take on Hugh McDiarmid’s poem A Drunk Man Looks at the Thistle.

She has founded her own opera company, Bloomsbury Opera, which stages one production per year. And she has commissioned and conducted two new operas, one from Scotland’s Anna Meredith, with the colourful title Tarantula in Petrol Blue, the other a chamber opera from Bulgarian composer Martin Georgiev, entitled Mirror, which Bulgarian State Opera in Sofia has expressed interest in transforming into a fully-staged opera next year.

Whatever way you turn it, Cottis is a young lady going places fast. But in fact she’s not in any hurry. Indeed, she had absolutely no intention of going into conducting. Daughter of diplomats in a musically aware family, she was primarily an organist, doing extremely well in her native Australia. Three things happened: she felt the need to move on from Australia, she damaged her hand and she spent a night at the opera.

It is possible, she says, to run the full educational gamut in Australia, and on into the profession; but there is a pull. “There’s always a craving for depth of culture and history, and we just don’t have that depth; so to come to Europe was an ambition.”

She went to Paris, studying organ with Marie-Claire Alain, and would have been content in that sphere, giving recitals and teaching. But pain overtook her, she was fearful of not being able to play and it was discovered she had Carpel Tunnel Syndrome: inflammation and damage to the nerves in the fingers.

“I was devastated; this was something I’d done all my life.” But she was also coolly pragmatic. She went to London and sought other pursuits that would challenge and engage her, including a study of law.

Then came the night of her life. She visited the Vienna State Opera which was performing Richard Strauss’s Der Rosenkavalier, and something happened. “Something just ignited in me. I’d worked with singers a lot and it struck me that conducting was a way of drawing all the strands together.” It wasn’t exactly a eureka moment, she says, but it triggered something. “It was an unconscious development – it was

germinating, surfacing slowly.”

But it was critical because it brought another issue to the surface in Cottis’s mind: “I was known as an organist. Is it possible to change career?”

She took lessons with veteran conductor George Hurst and began watching conductors, particularly those coming up through the Royal Academy’s “fantastic” conducting course, whose alumni include Ilan Volkov and ENO’s director Edward Gardner.

She applied for the course, got in, thrived, graduated and has been appointed a fellow at the academy, where she conducts the student contemporary music ensembles and does some work with the London Sinfonietta. Then along came Glasgow and its auditions with the musicians deliberately playing wrong notes in the Stravinsky test piece, testing her responses to see if she would be caught out. She got the post, was cock-a-hoop, checked with the Royal Academy to see if there was a conflict of interest (none) and is now in situ, beavering away assisting RSAMD head of opera Tim Dean in rehearsals for the academy’s epic production of Prokofiev’s War and Peace, running the academy’s repertoire orchestra through a private performance of Beethoven’s Eroica Symphony (directly from our interview) and dashing down to the City Hall to assist Ilan Volkov with last week’s BBC SSO concert.

The whole business of “assisting” big name conductors, she says, is as varied as the number of conductors involved, the venues and different acoustic spaces visited, and every factor involved in putting on a live performance.

“Standing on a podium as a conductor you hear a completely different sound than from outside in the hall. And you can never tell exactly how the audience will perceive it.”

And that’s why Runnicles, Tim Dean and the others want her there. That’s her function: it’s those “extra ears, hearing it from the outside”.

At the same time, she is practising her craft and art, soaking up the immense levels of experience to which she is being exposed.

She is absolutely loving it. She is an ultra-calm young lady – she’s not in a hurry and she’s not being rushed.

“I’m really enjoying myself. I’m making my own path, and it’s a really nice path to make. I feel that conducting is a slow-burning career. It’s not about getting out there and making a big splash, but developing it over time.

“The whole assisting thing for me is perfect. It gives me time to grow and think more deeply.”

When Donald Runnicles tells you he’s taking you over to Germany next week to assist him at the Berlin Phil, is that not the moment for a whoop of delight? “That’s the weirdest thing. I do have this bubbling energy of excitement, but it just all feels right.

“For some reason I’m not overwhelmed. I was when I got the call to say I’d got the job in Scotland. I remember jumping up and down on my bed for 10 minutes. Don’t quote that,” she shrieks with laughter, seeing yours truly corpse at the vision. Sorry Jessica, your cool is blown.