Orchestra of the age of Enlightenment/ Norrington, Queen Elizabeth Hall, London

The shock of the new Mahler

"Next thing you know, they'll be playing Mahler on period instruments!" Many a true word spoken in jest. Ten years ago "the Mahler experience" had reached such heights of virtuosity in concert that the idea we should go back on ourselves – that Mahler's vision for the future should be locked again into the past, that the orchestral hardware whose technical advancement was his dream might be "downgraded" so his early frustrations might be heard and felt – well, the very idea was laughable. But who's having the last laugh now? The irrepressible Roger Norrington, I shouldn't wonder.

That the period-instrument experiment has now come full circle is readily acknowledged by Norrington. But perhaps the biggest surprise is the extent to which it is the most recent music that has provided us with some of the most startling insights. Mahler has become less of a challenge for today's supersonic orchestras. They take it in their stride. With fabulous results. That's a fact. Mahler could only imagine what has become our reality. And yet the character, the colour and cast of his music is inseparable from, and perhaps even dependent upon, that sense of struggle, of instruments andplayers pushed beyond their natural endurance.

There are passages in his First Symphony – the centrepiece of this Norrington "Mahler experience" – that seek to change the world as Mahler heard it. He didn't mean for the opening – a brave new dawn, quite literally – to sound exquisite. Modern instruments can do that; they can play quieter and more beautifully in tune than Mahler could have imagined. But he didn't imagine that here; he imagined an eerie, haunting imperfection.

The Orchestra of the Age of Enlightenment are probably as good, if not better, than many of the orchestras Mahler worked with. But their instruments are no respecters of their virtuosity (horns and trumpets are particularly vulnerable); they dictate, to a great extent, the way they play. The excitement, the momentum, of this music was born of a strenuous endeavour. The coda of the first movement, with trilling horns more startling, more uncouth than their beefy modern counterparts can ever be, was properly reckless.

Later in this journey of rediscovery came the nasal, cadaverous double-bass solo leading our hero's funeral procession. No modern bass can even approximate to that sound. And those sleazy gypsy-band trumpets and trombones, heavy on the vibrato – the "V" word. Little or none of that in the strings, of course, but how honest and open-hearted that makes them sound.

An evening of tiny and sometimes not so tiny revelations, then. In putting the First Symphony in context with its original, sweetly old-fashioned second movement, Blumine, and the songs that gave it breath – Lieder eines fahrenden Gesellen – beautifully sung by Christopher Maltman, Norrington asked us to imagine that none of Mahler's later music had yet been written. Amazingly, we did and could.