“It’s those places where, in a strange way, I can step back. I’m participating, but I’m not having to bring any direction to the musicians, because their focus is perfectly calibrated. It happens constantly in concerts and rehearsals with this group.” He likens the experience to looking through a lens in which the images are absolutely clear. “You don’t need to fiddle with anything – you just have to admire the beauty that’s coming through that lens.”

Even from his first encounter with the Orchestra as guest conductor in 2003, the New York-based Robertson felt it had something special. On that occasion, he was in Sydney with his wife, pianist Orli Shaham, a soloist in one of the programs. “We had been married a total of six months at that point,” he says. “Everyone we met was so incredibly sweet and low-key in their way of behaving, but so tremendously professional and incredibly passionate about making the music. That’s a pretty incredible combination – it’s hard not to fall in love with it.”

That initial impression hasn’t wavered, says Robertson, who has been Chief Conductor and Artistic Director since 2014. He is convinced there are “certain projects and adventures” he wouldn’t have been able to do with other orchestras – the 120-musician Varèse Amériques, for instance, (“That was colossal”) or, on last year’s European tour, playing 12 concerts in 14 days. “I wouldn’t feel confident doing that with many orchestras, but the comfort zone of Sydney Symphony musicians seems to be extraordinarily high – there isn’t anything they can’t do.”

On the sound of the Orchestra, Robertson says it’s easy to generalise about something that’s immensely complex.

‘‘It’s the combination of everyone involved – they have a very warm sound, so even when they need to be harsh and abrasive, there’s a beauty of tone I love. Along with that warmth is an incredible muscular energy like the very best gymnast.’’

He heard that particularly clearly on the 2014 China tour, where the Orchestra played in seven halls. “It was like someone you know very well picking up seven different instruments. Hearing their personality being able to express itself in those different circumstances was revelatory.” It provided an impetus, he says, to work with others behind the scenes to “make sure the concert hall acoustics would be brought up to the standard of the orchestra”.

As a champion of new music, Robertson says one of the “really nice legacies” of his time in Sydney has been to introduce the work of Australian composers to overseas audiences. “I was at the Met Orchestra recently, and one of the players had heard Spirit of the Wild, the Nigel Westlake piece that Diana Doherty played – I was able to give him the CD. You have that aspect of proselytising, and the other side is that in Pittsburgh this season, I’ll be performing Georges Lentz’s Jerusalem. It’s very nice to be able to take those works around.”

He’s also taking more subtle things away with him. “When you work with musicians, you’re learning all the time. There are ways of turning a phrase or thinking about a sound that I have learnt from Umberto Clerici or someone like Andrew Haveron, ideas about percussion from Timothy Constable or Rebecca Lagos, or ideas about woodwind phrases from Todd Gibson-Cornish or Matthew Wilkie, just to name a couple of people. You never come back to those pieces without having that experience as part of their living tradition.”

Apart from the orchestra, there are other aspects of Sydney he’ll miss having regular access to, like the “very good food and coffee”, trips to the Blue Mountains, and walks around the city – “With its hills and various different vistas and the way it changes, for me it’s like an ever-evolving sculpture.”

Robertson is currently dividing his time between his role as director of conducting studies at Juilliard and guest conducting, with more opera in his calendar than he’s been able to schedule in decades. He’s looking forward to coming back to Sydney as guest conductor in July, and into the future, and “happily seeing everyone again. I’m very grateful for the depth of conversation we have had.”

On the future of the Sydney Symphony more generally, Robertson says, “I hope they keep their tremendous sense of curiosity and adventure – that’s a really prized commodity. In a place that has as much remarkable landscape as Australia does, to have a group that personifies that adventurous spirit is just wonderful.”