Chicago SO/Boulez/Barenboim, Royal Festival Hall, London

It was as principal guest conductor of the Chicago Symphony Orchestra that the now 80-year-old Pierre Boulez sprang lightly to the podium for this second concert of the orchestra's visit to the Royal Festival Hall.

It was as principal guest conductor of the Chicago Symphony Orchestra that the now 80-year-old Pierre Boulez sprang lightly to the podium for this second concert of the orchestra's visit to the Royal Festival Hall. Before launching into his all-Bartok programme, he gave a little speech to the packed hall, fondly recalling his BBC Symphony Orchestra days there 30 years ago and tactfully looking forward to the results of its impending closure for acoustic improvements.

Was this his way of warning that even the virtuosity of the Chicago players and his own legendary powers of clarity and precision were about to be sorely tested by the RFH's present miserable condition?

It was in the central item, Bartok's Piano Concerto No1 (1926), that the acoustic problems became most apparent. Admittedly, Bartok himself hardly makes matters easier to balance by pitching much of the orchestral detail in this score in the same middle range as its ferocious piano part. Nor did the Chicago SO's current music director, Daniel Barenboim, as soloist, make it easy for Boulez to follow his impulsive rendering. As a result, a work notorious for its uncompromising, steely constructivism came over as strangely blurred and opaque.

Fortunately, not even the shallow ambience of the RFH could neutralise the sumptuous and weighty scoring of the opening item, Bartok's substantial Four Orchestral Pieces (1912), dating from the same period as his opera Duke Bluebeard's Castle and with something of the same fierce glamour and fathomless sadness. Boulez has striven to establish this masterpiece in the repertoire and it was good to hear his unfolding of its almost symphonic progress from its luxuriant opening prelude to shuddering funeral march finale.

It was good, too, to hear the latter-day Boulez, so much less rigid and more spontaneous, directing Bartok's Concerto for Orchestra (1943) - a work once criticised for backsliding from the hard-line modernism of the composer's middle years. Actually, it represented not only a successful broadening of Bartok's idiom, but a triumph of his spirit over exile, privation and failing health.

And from the mysterious hushed opening, by way of the humour of its second-movement wind duets and the impassioned elegy of its slow movement, to its whirlwind finale, it was this range of human experience and sweep of spirit that most enlivened about the Chicago SO performance.