You’ve never seen so many people at a Prom, thousands of them packed into every space of the Albert Hall inside, while outside a 100-metre line of hopefuls queued in vain to stand in a pit where a small cat couldn’t have been added. But then this was a luxury Prom: with the Vienna Philharmonic and two musicians of golden integrity and sensitivity, lifetime members of the high table, the pianist Murray Perahia and the conductor Bernard Haitink playing two works born in Vienna.

If you’re going to bash a tam-tam for six, the Albert Hall is the perfect place to do it. The reverberation lasts for ages; and everyone in the audience can see you bashing. That must explain in part why Messiaen’s hieratic, gong-crazy Et expecto resurrectionem mortuorum has notched up 10 Prom performances in 45 years. Sunday’s was the first, though, to be performed by the historic and wonderful Leipzig Gewandhaus Orchestra, an outfit previously associated more with Bach and Mendelssohn than Messiaen’s idiosyncratic altar cloths in sound.

I'd love to see the stats on the last time a Prom was this packed for an afternoon organ recital. Were it not for the fact that organist Cameron Carpenter was sporting spandex trousers encrusted in silver glitter, a wife beater and Mohawk, you could have been mistaken for thinking we were back in the organ glory days of the early 19th century. Even the programme harked backward, offering as it did big, bloated Romantic transcriptions, arrangements and improvisations (pretty much everything in fact except the urtext).

“Well that was bloody fantastic,” a broad Aussie accent declared from somewhere behind me at the end of Ravel’s String Quartet in F major. And that’s the thing with the Australian Chamber Orchestra – it’s just that simple. Their concert programmes reliably include all manner of arrangements (the quartet, for example, was a classic Tognetti reworking for string orchestra) and unexpected collisions of repertoire, but strip all the tricks away and get them stuck into a serious bit of music-making and the result is thrilling and entirely unaffected.

Champagne on ice in the private boxes; scarcely any spare seats. This isn’t the normal situation for a concert climaxing in Witold Lutosławski’s Third Symphony, a modernist work whose usual audience is more than two men and a dog but still doesn’t pull in the crowds.

It's not completely unheard of what Sir Simon Rattle did at the start of last night's Prom, where he elided two familiar works - Ligeti's colouristic classic Atmosphères and the Prelude to Act One of Wagner's Lohengrin - into a seamless whole, beating without stopping from one into the other. But it was still pretty breathtaking.

Eric Whitacre – less a composer or conductor, more a global choral phenomenon. Just the mention of his name in last night’s concert introduction drew whoops and wolf-whistles from the crowd, certainly not a reaction you tend to get for Beethoven, Boulez or Cage (though perhaps the latter gets a silent cheer). Like or loathe the hype that surrounds Whitacre, there’s no denying his role in popularising choral singing, nor the pure American genealogy of his style, which we can trace back through Morten Lauridsen and Randall Thompson to Bernstein and even Copland.

In a festival season as long as the BBC Proms there are always going to be some longueurs, weeks where the orchestral playing is more adequate than astonishing. Get stuck in one of these and it’s easy to start doubting your ears, to wonder whether six weeks of orchestral assault have dulled them. Then you hear an ensemble like the Gustav Mahler Jugendorchester. A youth orchestra in name alone, there is nothing callow about this elite group of young musicians, who last night under Daniele Gatti coaxed and wrung the Royal Albert Hall audience into ecstasy upon ecstasy.

After the all-singing, all-dancing, all-helicoptering brilliance of Stockhausen Mittwoch aus Licht, the dry routine of an opera in concert didn't seem a very enticing prospect.  That's the problem with this year's Cultural Olympiad. We're becoming very spoilt by it. What should have been a mouth-watering prospect - a fantastic cast performing a great opera - suddenly began to feel run-of-the-mill when compared to the once-in-a-lifetime event that was Mittwoch. But my concerns were short-lived.

Théodore Dubois: Piano Concerto no 2, Ouverture de Frithiof, Dixtuor Les Siècles/François-Xavier Roth (Musicales Actes Sud)