Leopold Trio / Paul Lewis, Wigmore Hall, London

In August 1946, the 71-year-old Arnold Schoenberg suffered a cardiac crisis so severe that his pulse and breathing ceased, and he was only brought back from death by an injection directly into the heart. Yet, such was his creative vitality that, by the end of September, he had transmuted the experience into his 20-minute String Trio - one of the most radical scores of his entire career.

The challenge lies not so much in its 12-tone technique or the weirdness of its virtuoso sound-effects evoking the near-death state, but in its elliptical continuity. Gone are the orderly post-Brahmsian thematic groupings and transition passages still to be heard behind Schoenberg's Piano Concerto of only four years before. Instead, there is continual, nervy cross-cutting of disparate materials, eerie atmospherics, fierce onslaughts, ghostly echoes of tonality, with more lyrical passages constantly threatening to fragment or lapse into silence.

Because of its extreme technical demands, the work has tended to be performed, when at all, by ensembles specialising in hard-edged avant-garderie. So one was particularly curious to hear what the Leopold Trio, so warmly identified with their classical repertoire, would make of it - especially as they have recently acquired a formidable new violist in Lawrence Power. Nor did they disappoint. No doubt the intensive preparation for their forthcoming Hyperion recording helped, but the result was by far the most meaningfully nuanced, cohesive and sheerly musical live performance this pair of ears has ever heard of it, with its mesmeric final fade-out stilling even the most disaffected listeners in a packed Wigmore Hall.

The Leopolds already have successfully recorded Mozart's two innovatory piano quartets - the darkly angular G minor, K 478, and the more concerto-like E flat, K 493 - with that pellucid and affecting young pianist, Paul Lewis. In returning to them live, they once more contrived to maximise the contrast in character between the works, qualified only by a certain boomy preponderance of piano volume - at least, as heard from the back of the Wigmore Hall - which might have been mitigated by lowering the piano lid halfway.

Yet the other revelation of this concert was Schubert's only completed string trio, in B flat, D 581. Composed with some care and much redrafting in 1817, when the composer was 20, this concise four-movement piece is generally accounted charming, but relatively lightweight. Yet, by manifold inflections of pacing and phrasing, and some marvellously subtle modulations of vibrato and colour, the Leopolds showed the work's cheerful progress to be shadowed by more ambiguous turns of tonality and expression - sounding, indeed, little short of a masterpiece.