Prom 20: Northern Sinfonia/Zehetmair <br></br> Prom 21: BBC SO/Brabbins/Mullova <br></br> Prom 22: Blazin' Fiddles/Roby Lakatos Ensemble, Royal Albert Hall, London

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The afternoon concert moved on to two movements from Hartmann's Second Sonata for solo violin, from Thomas Zehetmair. If the first felt mechanistic, the second combined graceful arcs of melody with subtle timbral games. Then Zehetmair was joined by Viktoria Mullova for a rare Bartok treat. 44 Duos for Two Violins was the composer's response to a request to arrange his piano music for two violins. Bartok's genius was unleashed in new ways: here, we got 11 gems from this delightful work.

Zehetmair was then joined by the Northern Sinfonia for a nicely balanced performance of Vivaldi's Cponcerto for Four Violins and Cello,and then of Grieg's From Holberg's Time, and Britten's Simple Symphony.

It's hard to imagine a composer today writing The Young Person's Guide to the Orchestra, as Britten did for the Ministry of Education in 1946: here, in the evening Prom, it was a reminder of how didactic attitudes have changed. Then we got its contemporary equivalent Invisible Lines, a work devised and performed (without conductor or score) by a talented posse of teenagers. The piece had shape and thrust, and climaxed in controlled abandon: bravos all round.

The late Prom was the predictable rounding-off, with fiddlers from Scotland and Hungary. Blazin' Fiddles purveyed reels, dances and transposed pipe tunes: as wholesome as home-baked bread, and about as interesting. But when Roby Lakatos spun out his first cadenza, the earth stood still. His band are Gypsies like him, and each can carry an evening. Lakatos left us with birdsong in our ears.

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