The differences in quality between the two halves of Friday night's concert in the National Concert Hall were perplexing. The National Symphony Orchestra played a programme of Czech music under the Czech conductor Libor Pesek, who appears regularly with some of the world's leading orchestras and has produced some acclaimed recordings. The line-up read like a sure-fire recipe for success.

So it was disappointing to hear the strings of the NSO play Suk's Serenade for Strings with such raggedness of detail. This nullified the possibilities suggested by the light and shade which the performance sometimes achieved.

Dvorak's Violin Concerto was worse, largely because of persistently over-inflated playing. This flawed, too-densely scored piece can be engaging, but only if it achieves weight occasionally and through contrast. It was not helped by the solo playing of Dong-Suk Kang, which was over-accentuated in rhythm and had a nervous edge which made virtuosity seem desperate rather than elevated.

The second half of the concert opened with a minute's silence to honour the NSO's former trumpeter and recent management assistant Szabolcs Vedres, who had died that day. The playing which followed was in a different league from anything heard before; and the muscular styles of Martinu in Three Frescoes of Piero della Francesca and Janacek in Taras Bulba can be only a partial explanation for this disparity.

Whatever the reason, these performances had a definition which the Suk and Dvorak did not even approach, and they did so despite occasional problems with orchestral balance. Libor Pesek was a master of timing in Janacek's calculated discontinuities; and the NSO was with him all the way in that respect and in the vivid colour the music needs.