L'incoronazione di Poppea
Barbican EC2

Itzhak Perlman
RFH, London SE2

Vermeer Quartet
QEH, London SE1

Correct me if I'm wrong - no doubt you will - but I believe Monteverdi's L'incoronazione di Poppea is the only opera in which the baddies get away with it, apparently living happily ever after.

So where were they? Why did the Thétre des Champs-Elysées send two substitutes to sing Nero and Poppea in an otherwise sumptuous rendition, led by René Jacobs and his Concerto Vocale?

And another thing. If the Thétre du Chtelet can transport José Montalvo's brilliantly complex staging of Rameau's Les Paladins from Paris to the Barbican, why can't David McVicar's production make the same comparatively short journey?

These were the questions hovering over a generally ravishing, semi-demi-staged performance of Monteverdi's masterpiece, marred only by the fact that the two main soloists sang from scores. You could tell the rest had recently performed it together onstage; Anne Sofie von Otter, in particular, made an Ottavia as hypnotic for her magnificent hauteur as her sinuous singing.

Countertenor Lawrence Zazzo also invested Ottone with as much feeling as eloquence; in lesser, multiple roles, the tenor Tom Allen and countertenor Dominique Visse injected some welcome humour into the proceedings. With most of the cast acting their parts, however, and the two principals wedged behind music-stands, this supremely sensual piece was robbed of much of the theatrical impact it needs to rise to its true heights.

An announcement before the performance thanked the sopranos Veronica Cangemi and Zoryana Kushpler for coming from Paris to make up the numbers; to be fair, they did more than that. As Poppea and Nero respectively, both sang respectably, even beautifully, in the ethereal love duet which always seems so long coming - but how could either compete with Carla di Censo's scorchingly sexy Drusilla?

With the work's centre of gravity shifted towards its sundry sub-plots, thanks to the greater commitment shown by the rest of the company, this was a decidedly skewwhiff reading of one of the great artistic monuments to the triumph of passion over reason. You couldn't help thinking that the losers were the ones who should be stewarding Rome towards its inevitable doom; this semi-detached pair of imperial lovers looked like billing and cooing their way less towards Gibbon than Mills and Boon.

Ah, the pity of it, for Jacobs wrung the most shimmering, sensuous array of sounds from his plucking, twanging, glistening ensemble of players. Those who booked because of the Barbican's 'Great Performers' billing, however, were entitled to feel short-changed.

The reverse is true of those who went to the South Bank for one of the highlights of its International Chamber Music Season, Itzhak Perlman's only London appearance of the year. Before bringing a packed Festival Hall to its feet for the first of several prolonged standing ovations, the great violinist had them rolling in the aisles. After the red meat of his programme - Beethoven, Franck, Debussy - Perlman turned cabaret artist to wisecrack his way through a high-calorie selection of virtuoso bonbons.

The robustness of Perlman's inimitable playing had been evident in an impassioned account of Beethoven's Sonata No1 in A, his lyricism and spiritual depth in searching readings of the Franck and Debussy sonatas. Extraordinary technical expertise was, of course, as much on display as bottomless pits of feeling - but nothing to match the party-pieces which followed, from Kreisler to Ibert to Heifetz to Tchaikovsky, with a deadpan commentary worthy of Jack Benny.

'It says here that this piece is very difficult,' he mused, riffling through a selection of scores, 'so we won't play it.' The next one? 'For advanced players only. Better not try that, either.' The maestro's only missed beat was a clunky pun while translating 'Chanson sans paroles'.

With effortlessly fine accompaniment from the Italian pianist Bruno Canino, Perlman demonstrated yet again that he is without peer among current violin virtuosi. And the genial rapport he established with the vast audience the minute he opened his mouth - which so few instrumentalists ever do - helped all present understand exactly why.

If personality is a quintessential part of a great musician's make-up, the art of ensemble chamber music is to retain just the right amount while submerging the rest into a collective whole. 'Sometimes we disagree strongly, even after a performance,' says Shmuel Ashkenasi, leader of the Chicago-based Vermeer Quartet, 'but that doesn't mean we don't speak musically with one voice.'

Also part of the South Bank's International Chamber Music Season, the Ver meer gave a wonderfully warm, rounded account of Haydn's B flat major quartet, a thrillingly impassioned reading of Shostakovich's fifth, and a magisterial performance of Beethoven's in C major, Op59 No3. Here is a group of outstanding musicians from three countries - one Israeli, one German and two American - who have worked their way towards a mutual understanding as bewitching to behold as to hear.

Each looks very different, with contrasting platform styles, yet the musical union they achieve is quite wondrous. Decorous, modest, immaculate, reminding us that great artistry can also entail wholesale suppression of the ego, these supreme chamber musicians are enough to give absentee opera singers a bad name.