"This was a live concert in 2013 with the Vienna Philharmonic," he says. "Amusingly, it was the orchestra's first performance of the concerto: strange, when you consider Schoenberg had been working in the city for all those decades and wrote it back in the mid-1930s."
Working with the legendary Boulez - who passed away earlier this year, aged 90 - was an unforgettable experience, says Barenboim. "He was so friendly and nice but also demanding, always in an atmosphere of great serenity."
Barenboim is proudly playing Boulez's own Anthemes I in an Australian recital tour later this month, alongside other unaccompanied music by Bach and Bartok.
Boulez himself worked with Barenboim on his 1991 piece and, although I'm told the Frenchman had his humorous side, Barenboim stresses he was also very serious.
"Especially when it came to preparing yourself for a performance and knowing the score scrupulously," he says.
Boulez, writing on Schoenberg in 1974, draws a portrait of a man weighed down by his prophet status, trapped between the uncontrollable admiration of his disciples and the equally excessive hatred of his opponents. I ask Barenboim how he feels about American composer and writer Aaron Copland likening Schoenberg to a musical equivalent of the Russian politician Alexander Kerensky, "unable to carry through the full implications of the revolution he himself had instigated".
Barenboim concedes that Schoenberg's Concerto is "not exactly Brahms" in terms of popularity, but feels there are strong links between the two composers.
"Schoenberg looks back to Brahms for a new way into the future," he explains, citing the concerto's very romantic first movement as an example.
"While Schoenberg was always progressive, his compositions are always tempered by a deep respect for and understanding of tradition. This is music that doesn't disregard its roots and sources."
Why then, I ask him, even half-a-century after Schoenberg's death, are some listeners so wary of him?
"There are many other composers who have written much more difficult music, but don't incite the same fear factor. Perhaps Schoenberg's single-handed breaking down of the traditional tonal system is the reason. Some listeners are so attached to the tradition of major and minor harmonies that they feel threatened if it is broken."
Barenboim suggests other Schoenberg music that could provide useful context for Thursday's concerto, from the early Verklarte Nacht to the much later Ode to Napoleon, climaxing after 15 minutes of spiky dissonance on a triumphant major chord.
"Schoenberg never stopped writing tonal music," Barenboim insists. "He wasn't trying to destroy it. It was a necessary step in moving just that much further than his predecessors."
Performance
What: Auckland Philharmonia Orchestra - Degenerate
Where and when: Auckland Town Hall, Thursday at 8pm.
