With the Los Angeles Philharmonic, the transaction between conductor and orchestra was heightened by professional rank. World-class players gave Dudamel the same emotional response as his compadres and, over cocktails at the bar, gushed about him like teenaged groupies. The added value, for Dudamel, was that with LAPO he could leap without a parachute.

While rehearsing the Sixth, he called me in for a chat about the order of the inner movements — Mahler published them as Scherzo-Andante but performed them in reverse — and whether there should be two or three hammer blows in the finale. Again, Mahler was in two minds. "Make it work," he told future interpreters.

"Which is it?" said Gustavo.

"Do as Mahler would have done," I advised. "Go with the feeling."

So he did. In rehearsal he tried the inner movements in both orders, settling for Andante-Scherzo but still prepared to change his mind. As for the hammer blows, he devised a secret signal to tell the percussionist which it was going to be, two or three, delaying until the last possible moment. 

I have never known a conductor jeopardise a whole cycle on a late whim. But it is faultlessly authentic, exactly what Mahler would have done. By upping the ante on the hammer blows and deciding in the end on two, Dudamel changed the character of the Sixth Symphony finale from unrelieved doom to a glimmer of hope. Hundreds in the audience stayed on afterwards for half an hour to discuss with me the remarkable transformations they had just heard.

"In Mahler," Dudamel said as we parted, "you see complete transcendence — how a man's life is transformed from the First Symphony to the Tenth. Everything undergoes metamorphosis." I flew home to London. He went on to Caracas, to deliver an Eighth symphony with 1,400 performers, the largest yet. There was a historic dimension to this project, much of which will be released on video. It will not silence endemic mutterers, but I saw enough in a week to support the assessment five years ago of a veteran US concertmaster, a hard-hat who has chewed out more young conductors than I have written 1,000-word columns. "Don't bracket Dudamel with the rest, Norman," he warned. "One like this comes once in a lifetime."