As Marin Alsop tells it, it's rather like a fairy tale. She went to one of Leonard Bernstein's Young People's Concerts at the age of nine, and had an epiphany. Conducting was what she wanted to do.

“I imagine it’s like when someone has a religious calling, and they just somehow get this lightning bolt,” she says. “It was a very immediate, visceral reaction to the experience. In hindsight, I think what grabbed me was his enthusiasm, his sharing of that enthusiasm with the audience. He spoke at the concert, which I’d never seen a conductor do before. I had the feeling, being nine, that he was just speaking to me, directly.

“As I’ve thought about it over the years, there are all sorts of other skills involved and disciplines involved in becoming a conductor that have appealed to me. Needing a very broad range of knowledge, contextual knowledge, is something that always appeals to me. I love reading, history. The psychological, societal dynamics of conducting appeal to me.”

Alsop played violin in orchestras at the Juilliard School from the age of seven, and her parents, both professional musicians, gave her every encouragement. But she also registered from the outside world that she was too young, and that “girls don’t do that” – a dictum she has forcefully helped to overturn. She never wavered, and she now tests her students to see “whether they have the skin thick enough simply not to give up what they’re doing. Conducting is a long journey, and if you’re going to waver at every corner, you’re never going to make it. You have to put your head down, and go one step at a time.”

When she played in the Mostly Mozart Festival or deputised with the New York Philharmonic, she always asked the conductors for lessons. “I have to tell you that no one ever said no, though I was too afraid to ask Klaus Tennstedt. He was not in the greatest shape.”

In her 20s she started her own orchestra with friends, who were “extraordinarily helpful and constructive”, teaching her not to be apologetic or deferential, helping her to sharpen her communication skills, and letting her know “we like you, so you don’t have to try to be liked”.

Most of the skills of a conductor can be taught, but not everything. “It’s a microcosm of who you are as a human being,” she says. “And that you can’t fundamentally change. You can change how people perceive you, and you can change your behaviour. But, fundamentally, who you are is who the musicians see.”

She recalls Maurice Abravanel – who gave her father his first job with the Utah Symphony Orchestra – talking to her at the Tanglewood Music Center in Massachusetts. “He came up to me and he said, ‘you have a beat that musicians want to play for’. I didn’t really know what that meant. But now that I’ve taught so much, I understand that there are some people who have an organic, natural beat, that musicians find easy to follow. I don’t know if that can be taught. That’s something instinctual.”

And the best lesson she ever learned as a conductor? It was at Tanglewood, when she was being coached by Bernstein in that rugged, 20th-century American classic, Roy Harris’s Symphony No 3. “He came up to me quietly when I was conducting and said: ‘It’s all very correct. But there’s something missing.’ I thought: oh my God. I’ll just kill myself now. We gave the orchestra a break, and I went outside, thinking: what am I gonna do?

“I remember it like it was yesterday. It was a lovely day, the trees were so beautiful. I thought: I’m doing the thing I want to do, I don’t think anyone is more fortunate than I am. I’m just gonna enjoy it. I went back in and felt like I’d had a massage or something.

"I didn't worry, I just tried to be the music. And he came up when I was 20 bars into the piece, and he said, 'That's it. Just for yourself.' You know, technically you want it to be right, and at the end of the day all that really matters is to be totally present in the music."

Having been at the helm of orchestras in Colorado, Baltimore and Bournemouth, South America was not really on her radar when she had her arm twisted to conduct Mahler’s Seventh Symphony in São Paulo.

She liked the orchestra, and she liked the hall. “And within one rehearsal it grew exponentially. They were very responsive, really into it, the musicians. I met the management team and some board members.”

She describes them as “Renaissance people”, versed in any number of disciplines. “The busy people are the ones you need to do the work. I remember thinking: this is an incredible opportunity for someone. What interests me are attitude and passion more than anything else. They had that in abundance. A board member said to me, ‘It’s a shame you wouldn’t be interested in this job’. I said, ‘I don’t know. Maybe I would.’ And that started the discussion.”

Marin Alsop conducts the São Paulo Symphony Orchestra in Clarice Assad's Terra Brasilis, Bernstein's Symphonic Dances from West Side Story, and Mahler's First Symphony at the National Concert Hall on Saturday. nch.ie