It seemed strange that Pierre Boulez should be absent at his own 90th birthday celebrations, especially those of an ensemble with whom he holds such a strong connection. Having been closely involved with the ensemble during the 1960s, Boulez was appointed Chief Conductor of the BBC Symphony Orchestra between 1971 and 1974. He was widely considered to have raised the standards of the ensemble, who gave a number of premières of Boulez's own music. Comprising of two films, three concerts and a talk, the BBC Symphony Orchestra's Total Immersion day could only ever scrape the surface of Boulez's contribution to music. The selected works emphasised the longevity and the range of his musical output, ranging from 1945-2005. The lunchtime concert featured Boulez's Piano Sonata no. 2 (1947-1948) and his Éclat/Multiples (1965, 1970), offering a glimpse into the composer's aesthetic stance at three different moments.

Boulez's formidable Second Piano Sonata is often described as a violent and furious work, with its notes seemingly poured out in an impassioned outburst. Of course, this is far from the case: although the work is clearly confrontational, its carefully crafted structure demonstrates his understanding of the musical ideals he was intent on bulldozing. However, the provocative side of the work is matched by a frequently overlooked poetic dimension. Jean-Frédéric Neuburger drew attention to this aspect of the work, emphasising expressivity without compromising its unyielding nature.

Throughout, Neuburger was careful to draw attention to the structural boundaries on which the work was constructed. He highlighted the structural junctures of the sonata form first movement, providing clear reference points within the stream of notes. Neuburger's interpretation of the Lent was almost Romantic in nature, utilising rubato and dynamic swells while placing the notes carefully and softly. Lending weight to the silences of the third movement was greatly effective, underlining both its emotional content and its tight construction. Unfortunately, the vivid detail which had made the former movements so engaging was absent from the finale; interestingly, though, the coda was almost nostalgic in Neuburger's hands.

It was refreshing to hear the Sonata performed as a musical statement, rather than merely an aesthetic one. Neuburger's expressive approach was rather more effective, negotiating with the past before rejecting it, instead of erasing it with brute force. It was a shame that the tautness of his interpretation was diminished by the final movement, but his was a refreshingly flexible approach nonetheless.

Éclat/Multiples is, by all purposes, an incomplete work. Boulez originally envisioned adding to the pair, composing further episodes with expanded length and instrumentation. The BBC SO have a particularly strong relationship to the work, having given the world première in October 1970 under Boulez (although Éclat had been premiered in Los Angeles, 1965). The pair demonstrate Boulez's virtuoso control of the orchestra through timbral play, pointing towards the fluidity and voluptuousness of his later works.

Éclat is an example of Boulez's dabblings in aleatoric music: the performers choose the speed and the order at which they perform certain figures. Just ten minutes in length, it explores the sonic characteristics which can be extracted from a group of 15 instruments. The eclectic ensemble, which includes mandolin, cimbalom and vibraphone, is divided into those instruments which are able to sustain and those whose sounds are produced by percussive means. The work explores the resonance of bright, bell-like sounds, with tubular bells appearing at a number of structural peaks. Boulez explores the distinctions between instruments, blending together harp and celeste, glockenspiel and cymbalom as ideas dart around the ensemble.

Multiples introduces nine violas and a basset clarinet to the ensemble. These darken the sound-world and introduce an extended melodic element, dissipating the attack of Éclat for a more continuous approach. Pedals emerge and recede, gathering melodic ideas around them. Multiples may not be as tightly wrought a work as Éclat, but it is fascinating to trace the relationship between the two, and to consider the directions that any subsquent material might have taken.

The BBC Symphony Orchestra players gave a more dynamic performance in Éclat: its sequel lacked the same level of intensity, and the violas seemed slightly feeble. As a late stand-in for Francois-Xavier Roth, conductor Pablo Rus Broseta's direction was particularly admirable (especially given the unusual role required for Éclat), his firm, arching gestures a good fit for the former piece. Éclat/Multiples was a fitting conclusion for the first concert of the day, providing food for thought, but leaving much more to say.