LENOX -- Don't worry about the audience, Phyllis Curtin tells a student. If you think about the audience, of course you'll get nervous. "Sing it to the universe!"

This is Curtin's 50th season of master classes at Tanglewood. The former opera star and recitalist, now 91, has been through a maze of health setbacks, including severe arthritis, in recent years. Undaunted, she's teaching from a wheelchair.

To another student, she says: Get the words out more distinctly; the words are why the song exists.

"My voice has gone to sleep," another student worries. With pointers on the anatomy of breathing and muscles, Curtin wakes the voice up.

By happy coincidence, 2013 is also the centennial of Benjamin Britten's birth, which the Tanglewood Music Center is celebrating with a staged production of his opera "Curlew River" and a selection of his other works. Britten stands large in Curtin's career.

In 1946, the first of her three summers as a Tanglewood student, she sang in the American premiere of his "Peter Grimes." Then in 1963, in the midst of a lustrous career, she returned here as a soloist with the Boston Symphony in the American premiere of his "War Requiem." To this day, she describes the pacifist work as one of the most meaningful things she has ever sung.

It was that performance that led to her 50 years of seminars. While here in 1963, she taught a few classes. The next summer, she returned to begin her summer-long sessions. Along the way, as the singing career tapered off, she became a teacher and administrator at Yale and Boston University.

There are a couple of other coincidences. John Oliver, founder and director of the Tanglewood Festival Chorus, is also marking his 50th Tanglewood season. Curtin and he have been colleagues all those years. And up the road a couple of miles, Shakespeare & Company is presenting Terrence McNally's "Master Class."

Based on the classes Maria Callas taught, the play portrays Callas as a vain and egotistical, if pathetic, bully with students. Suitable theater, perhaps, but not the way it's done. As Callas did, Curtin lavishes praise and tries to bring out the best in the student. She also invites the class to join her in critiques.

Let others play the diva. For Curtin, it's all in the music.

This is also an emotional time for Kazushi Ono, the Japanese conductor who makes his Tanglewood debut with the BSO tonight.

It was 30 years ago that he came to Tanglewood as a conducting student. It's a thrill to be back, he said after his arrival this week.

"It was an amazing period," he recalled. He studied under Leonard Bernstein, Seiji Ozawa and Leonard Slatkin. The program was "very tough sometimes but very professional."

Now principal conductor of the French National Opera in Lyon, Ono also becomes director of the Tokyo Metropolitan Symphony Orchestra in 2015. He made his BSO debut in 1999 as a substitute for Daniele Gatti.

"He made a very good impression, and has got a beautiful and clear technique and is very musical," said BSO artistic administrator Anthony Fogg. The BSO had been thinking about bringing him back but couldn't the opportunity till now.

Because of the Japanese connection, "we, of course, had to talk to Seiji about this," Fogg said. Ozawa was "very enthusiastic about having him come to us."

In Japan, Ono said, he has worked several times with "Seiji-san," conducting at Ozawa's Saito Kinen Festival in late summer. Because Ono's career has mainly been in opera, Ozawa asked him to conduct in a twin bill of Ravel operas this year, but a conflict of dates made it impossible. Ono will conduct an orchestral concert instead.

"It's a great opportunity for me to conduct such a wonderful orchestra," he said.

At Tanglewood, the newcomer will lead a program of Wagner, Ravel and Rimsky-Korsakov's "Scheherazade." He notes that his Wagner, the "Siegfried Idyll," performed as part of the Wagner bicentennial, will show the composer's more intimate side. Pianist Leon Fleisher will be the soloist in Ravel's concerto for the left had.

Fleisher may not remember it, Ono said, but back in the 1980s he once served as page turner for the pianist. Ono is looking forward to the collaboration.

One more thing about Ono. He's not related to Yoko Ono. In Japanese, he said, the names aren't even pronounced the same.

Fleisher is in retrospective mode as his 85th birthday, on July 23, approaches. Sony has just released a boxed set of 23 CDs encompassing his entire recorded output. The albums begin with a solo Schubert disc originally issued in 1956 and end with three Mozart concertos released in 2009.

The recordings join his memoir, "My Nine Lives," published in 2010. It includes an account of his ups and downs with Ozawa and the BSO over the years.