You cannot imagine just how much is riding on Aaron Copland's Fanfare for the Common Man until you hear it in its proper context: at the portal of his Third Symphony's grand finale. At first it's little more than a glimmer, an anticipation, flutes and clarinets like spring awakening. But a sudden groundswell of string basses brings trumpets and tub-thumping drums in their wake and before you know it this Olympian rallying call has all but outgrown the symphony it engendered. Because this is where it all began, this is the source of its vaulting ambition, its wide-ranging thematic intervals, its bracing, open harmonies. This is the house that Aaron built. And it's a skyscraper.

Actually its foundations went down towards the close of the Second World War, so in a sense it was a rebuilding exercise, an attempt to re-unite Americans, to bring the nation together again: one nation, one voice, one creed. Hence that fanfare. Hence the symphony's consonance, its emphasis on "simple expression", honest and homespun. Michael Tilson Thomas spoke rather touchingly of its idealism just before his cracking performance at the Barbican last Thursday. And his words had barely time to register before the London Symphony Orchestra - not least their handsome, big-boned brasses - began shifting those hefty sound blocks into place. Side-drum rim-shots and hell-raising trumpets herded up and moved out the scherzo's cowboy song, and Tilson Thomas really went for the uplift of the coda where the gentle trio theme gets to join the cowpunchers in a jubilant full-blown canon. It's always singing at the top of its voice, this symphony - literally so in the dreamy slow movement where Copland's violins seem to graze the outer edge of the stratosphere. The LSO strings - indeed the entire band - were totally unfazed by the high tessitura of the piece. The snappy, latino syncopations came naturally, too. The finale was something of a sensation in that respect. One tiny quibble: Tilson Thomas might have landed more squarely on the pneumatic bottom D which anchors the final chord.

But hadn't we heard that coda, with its hammering anvils and proud tomorrow- is-another-day rhetoric, somewhere before? Actually, yes. A week ago in Leonard Bernstein's Second Symphony: "The Age of Anxiety". But then the spirit of renewal has a distinct sound in modern American musical literature. And besides, somewhere beyond all the post-traumatic stress, there's that place for us, that "Quiet Place". Sid Ramin and Michael Tilson Thomas's suite from Bernstein's opera of the same name gets better with every hearing. Ian Bousfield's agile and mellifluous solo trombone is now so much inside the central character of Sam that it is almost as if his anger and frustration were always beyond words. And it goes without saying that the LSO instinctively know how to swing the protracted shrug of the ironic "jazz trio". But it's the postlude, with its cathartic oboe solo, which takes us to the still centre of the piece - the quiet place, the refuge for Bernstein's art.

Every composer must find such a place. Mahler found it in the words of Friedrich Ruckert and the most beautiful of all his songs: "Ich bin der Welt abhanden gekommen". Thomas Hampson sang it here with quiet and sustained rapture. Earlier, one could perceive some evidence of the ailment that had brought about the last-minute cancellation of his solo recital last week. Such is the quality of this singer's honeyed legato that any inhibition of it is greatly amplified. But come the ringing endorsement of "Um Mitternacht" (with its extraordinary wind and piano colourations - far from seamlessly executed, it has to be said), the unwelcome residue in the voice seemed to clear, freeing it to explore the "tranquil realms" of that final song. At the last, violins glided upwards on the most fragile of glissandos, and it was as if they'd taken the voice with them. Suddenly there was no quieter place in the universe.