A piece of music written by a dying composer, left unfinished and completed by a dedicated friend from the chaotic fragments left behind. This is not just the story of Mozart’s Requiem, so familiar to many from Peter Schaeffer’s colourful retelling in Amadeus, but also of Bartók’s Viola concerto, which was imaginatively paired with the more well-known Requiem by Northern Sinfonia this evening.

The crowds who filled Hall One at the Sage were no doubt mostly there for the Mozart, so this was an excellent opportunity to give Bartók’s incredible concerto a wider hearing. The piece opened with Ruth Killius’s solo viola, playing a lyrical tune that becomes gradually more energetic and this opening section was accompanied only by the timpani, giving it the feel of Eastern European folk music. This folk theme becomes far more prominent by the end of the concerto, as the viola part turns into a blazing whirl of impossible virtuosity, accompanied by a rhythmic, syncopated drone on the strings and punctuated by blazes of colour from the woodwind. Although the beautiful second movement was more sombre, it was very hard to believe that this energetic and colourful piece was written by a dying man.

This was a piece that was eminently suited to Northern Sinfonia’s energetic and enthusiastic style, with ample opportunities for their very talented wind players to enjoy themselves. I was particularly impressed by the almost impossibly quiet trumpet playing in the second movement. Ruth Killius’s viola playing was astonishing and demonstrated the full capabilities of an instrument that is all too often the butt of musical jokes; the warm timbre of the lower register, and a big, bold sound on the joyful cadenza passages. It was however unfortunate that she stood sideways on, so that her face was completely hidden behind her hair, with the result that her fabulous playing lacked engagement with the audience.

Northern Sinfonia and Thomas Zehetmair brought the same level of fresh excitement to the Mozart Requiem as they did to the fast and furious Bartók concerto, aided by the impressive singing of the Northern Sinfonia Chorus. There can be a temptation to make the familiar opening chords too ponderous but tonight it was light and delicate and I almost didn’t notice that it had started. Throughout the work, the choir’s singing was disciplined, but never dry. Every consonant was perfectly enunciated, infusing sections like the Kyrie and, even more, the Rex Tremendae with electrifying power. The balance between the individual choral parts and between choir and orchestra was good, so that in the fugal passages of, for example, the Offertorium, each part could be clearly heard. The verve of the louder movements that tell of terror and the fear of eternal damnation contrasted with some lovely, tender legato singing in the more contemplative passages in which the focus is on prayer for mercy.

Andrew Foster-Williams, singing the bass-baritone solo was excellent in the Tuba Mirum solo; his voice had a rich power that was well suited to this majestic aria. The other soloists were a little weak, and seemed to struggle to fill the hall, although their ensemble passages were very well blended. The Mozart Requiem isn’t a piece where the solo singers have a big role to play, however, so this did not detract from the rest of the performance.

Although both of tonight’s works were completed posthumously, they both showed the genius of their composers to create such distinct styles that even fragments of their work gave their successors the inspiration needed to complete them. And Northern Sinfonia showed once again that whether you’re hearing them playing a well-loved classic, or a piece that was probably unfamiliar to most of the audience, you know you’re going to hear something new and and exciting from them.