Ivor Cutler called silence the music of the cognoscenti. But there's silence and there's silence, and a regular concertgoer hears a fair bit of both. The ability to fold silence into a musical line - to create the impression that a conductor is somehow sculpting a sound which doesn't exist - is an indicator of high artistry on the podium.

Conversely, there's the embarrassing strained silence when, at the end of a work, a conductor decides to keep the baton raised and see how long he can hold back the tide of applause. It's spray-on sublimity; an attempt to force the illusion of shared transcendence. It's the musical version of faking an orgasm.

The silence in the Royal Festival Hall at the end of Mahler's Ninth Symphony was of a different order. The conductor, Herbert Blomstedt, wasn't grandstanding. He'd conducted baton-less, sitting on a piano stool, and barely raising his hands above the level of his chest. And at the end, the intensity was absolute. When it's fake, there's always a giveaway; impatience prickles in the air and you can sense even small movements. This was real: the deep, concentrated hush of 2,700 people sitting and listening as if the silence was part of the symphony. There's no sound remotely like it.

Then the spell broke. Even for these ovation-happy times, the audience was quick to stand, and it's true that everyone present (including the players of the Philharmonia) will have arrived primed to expect profundity. Blomstedt - and there's no point hedging around this - is 97 years old, which is unusual even in a profession that places a premium on age. Leopold Stokowski was active until the age of 95, while Pierre Monteux signed a 25-year contract with the London Symphony Orchestra (with an option to renew) shortly after his 86th birthday. Disappointingly, he didn't quite make it to 90.

Is Blomstedt the oldest person to conduct professionally? It's hard to prove, though he's surely the oldest person ever to conduct an 80-minute symphony in public with an orchestra of international standing. So, what does a conductor of 97 have to tell us about a work that's often described as a 'farewell to life', composed by a man less than half his age? The main thing seemed to be economy - a stripping away of the non-essential. Mahler helps a conductor there: his scores are so full of nuances and instructions that they're basically huge interpretative cheat-sheets. Simply do what's printed and even without further input the results will sound expressive. That was all present, of course. No, the remarkable thing about Blomstedt's performance was what wasn't there. It was clear and unshowy, with none of the slightly gooey mannerisms that some maestros have convinced themselves represent authentic Viennese style. Where Mahler deployed a particularly pungent colour - a block of muted metallic brass, or that hectic glockenspiel in the third movement - Blomstedt let it ring rather than smoothing it into the mix.

There was no exaggeration. When Blomstedt opened up, he simply let the orchestra have its head, and the Philharmonia strings and horns surged in response. And when he did bring things right down, he drew the sound around him, refined rather than tense. The violas placed their last four notes against the coming silence like a sort of QED - a final thread tied, and a reminder that whatever else Mahler might have been implying, this was still a symphony; a creation of the intellect, as well as the soul.

I was reminded of Boulez. But also Karajan - not the man himself, but the critic who said of him that even if we never again hear something so extraordinary, we know now that it can be done.

The Royal Academy of Music's end-of-term opera came with a content warning: not suitable for the under-13s. That's not something you expect from Humperdinck's Hänsel und Gretel, but the production, directed by Jack Furness, placed the action inside a white box which turned red - a bloody chamber - to represent the witch's house. Blood oozed stickily from the children's dream-feast; Gretel was menstruating and traumatised, and the parents were abusive, misogynistic religious fundamentalists - the usual Handmaid's Tale drill. In this context, Humperdinck's tender-hearted hymns and folksongs offered very cold comfort.

It was a provoking, idea-rich staging, superbly realised but very consciously pitching the action against the score. That's routine in many German opera houses; and the RAM's function, after all, is to prepare its young singers for an international career. They sang admirably and Erin O'Rourke, as Gretel, could hardly have committed more fully to the role. As Hänsel, Clover Kayne's voice really blossomed after the interval. The orchestra might have benefitted from more string sectionals, but overall, this was an impressive night, as long as you'd left the kids at home.