Michael Tilson Thomas is celebrating one of the longest tenures of any music directorship in the contemporary world.

His leadership of San Francisco Symphony is longer than that of Seiji Ozawa with the Boston Symphony Orchestra, Simon Rattle’s with the CBSO, and almost certainly Rattle’s with the Berlin Philharmonic Orchestra.

He brings his San Francisco Symphony to Symphony Hall on Friday,

“Long-term musical relationships are very important to me,” he enthuses.

“Next year is my 20th season as music director of the San Francisco Symphony. I founded and have led the Miami-based New World Symphony for over 25 years, and have worked with the London Symphony Orchestra for the past 40 years.

“In all of these cases it’s been possible to work together with the members of the ensemble and the audience to explore the whole realm of music, arriving at a personal approach which grows and changes over time.

“With the San Francisco Symphony, I‘m very proud of the fact that, after almost 20 years of working with the orchestra, our relationship is the best it has been.”

The conductor insists that his relationship with the symphony is even better now than it was at the beginning of his tenure.

“I’d say it’s unusual in the artistic world, in the performing arts world, that after such a long time the people really have a greater affection and respect for one another than they did in the beginning. Part of what keeps it vibrant is our ability and desire to take risks,” he adds.

He describes what he sees as the particular strengths of the San Francisco Symphony.

“From the very first concert I heard the musicians play, I was aware of the daring spirit of the orchestra,” he says. “That’s been at the centre of our relationship. I continue to be excited and moved by the sheer brilliance, consistency, and elegance with which the orchestra is playing, week after week.

“The San Francisco Symphony is a collection of musicians who reflect the city in which they reside. San Francisco is well known for its broad thinking and widely varied population. Our musicians’ sense of adventure in performance reflects that same expansive spirit.”

Many years ago the conductor brought the London Symphony Orchestra to Birmingham Town Hall, and a veritable fan-club of groupies were dangling over the Lower Gallery. He was very much a young lion in those days. How does he, now an elder statesman, look back on such adulation?

“I measure success by how much we have touched our audience and how much we have expanded the opportunities for new listeners to join us,” he says.

“Extending music’s scope is vital to what we do, most of all, by making music in a generous and caring way. That’s the foundation of our partnership with our audiences.

“For me, making music is a journey I like to compare to going to a park. You may know the park, you know the trails. But the company in which you find yourself has a great effect on the nature of that journey.

“Over many years having walked these trails in these symphonies with my colleagues in San Francisco there’s a sense of ease of our ability to turn our attention to one thing or another while having the big objective of the journey in mind.”

Tilson Thomas and his San Francisco Symphony are bringing a fascinating programme to Birmingham, brimming with modernism – though the main offering is nearly 200 years old. This is the Berlioz Symphonie Fantastique, a work which rattled so many cages at its Paris premiere in 1830.

The conductor is in no doubt as to the symphony’s artistic significance.

“The Symphonie Fantastique is an orchestral spectacular and still the model of what a romantic symphony should be. It pours straight from the heart and soul of its composer. He wrote the symphony in a state of acute emotional distress, but its raw materials had been a part of him since the days of his childhood. With the Symphonie Fantastique Berlioz stepped into his artistic maturity.”

His programme begins with an item with which some purists might take issue. The Concord Sonata by the one-time insurance salesman Charles Ives is a pianistic Everest but Michael Tilson Thomas is proposing to open the evening with an orchestration of one of its Massachusetts-based movements, The Alcotts.

The conductor is a passionate advocate of this orchestration.

“In the case of Henry Brant’s orchestration of Ives Concord Symphony, this is a supreme tour de force of technical brilliance,” he declares.

“When Ives first wrote this piano sonata, few people took it seriously. His rhythmic ideas and harmonic ideas were very much ahead of their time – very challenging, very confrontational. Ives worked on this piece for decades – writing it, re-writing it, adding more and more levels of intricacy to it.

“Henry Brant worked on this orchestration of the Concord Sonata on-and-off for 50 years. He was a very skilful orchestrator. In fact, all of his avant-garde experiments in music were financed by his work as an orchestrator for Broadway shows and for movies. He applied this incredible skill he had in making an orchestra sound lush and wonderful and mysterious and spiky, to crack the code of the Concord Sonata.”

The concert also includes a recent work by the much-loved minimalist composer John Adams, his Absolute Jest for Orchestra and String Quartet, inspired by the scherzos of Beethoven’s late string quartets.

* Michael Tilson Thomas conducts the San Francisco Symphony at Symphony Hall on Friday, 7.30pm. Details on 0121 780 3333.