MUSIC / The long and the short: Nicholas Williams on the unknown Mendelssohn

Put it down to sibling rivalry, but this week's most exciting British premiere, an Overture in C, was by a girl. A taut, finely orchestrated structure, brimful of invention, its pacing and harmonic wit showed not just potential but genuine mastery. There were good tunes too. The composer - Fanny Mendelssohn.

As it happened, the Ambache Chamber Orchestra, giving the belated first performance, also contained a large contingent of female players. Sophie Langdon directed from the first violin desk both here and in the 'Prague' Symphony, and worked sympathetically with the ensemble's namesake, Diana Ambache, in Mozart's first and last piano concertos. A conductor's presence might have eased performance tension, giving the soloist more scope for fantasy, but that is not her style; the exercise was strictly classical.

Should the Ambache executants turn their skills and positive attitudes to the 20th century, they might consider the music of Hanna Kulenty. The complex formal schemes of her Sesto, played by pianist Andrew Ball at the ICA on 27 February, in no way inhibited the surface appeal of shining keyboard textures. Other highlights of this Gemini concert were David Lumsdaine's epic scena A tree telling of Orpheus, passionately sung by the soprano Mary Wiegold, and Keely Hodgson's abrasive string trio Surfacing. Pieces by William Campbell and Robert Godman played various minimalist games, a verbal equivalent of which may be recommended for Alwynne Pritchard's From this deposit a transparent bubble comes to the surface at certain times and explodes gently on reaching his lips, for bass clarinet (programme note equally opaque).

Long names remain one way of grabbing attention. Reservoir, however, a group fresh to the contemporary scene, are pursuing their new music adventures under a shorter title. Their particular store, to judge from last Thursday's recital at St Giles, Cripplegate, is one of talent. Disciplined brass litanies gave weight to Xenakis's brooding Epei; Ornette Coleman's jazz fiesta, The Country That Gave the Freedom Symbol to America, was directed with intelligence and enthusiasm by Mikel Toms. Nyman, Scelsi and Zappa are some of the names in forthcoming concerts. Warmly recommended.

The Nash Ensemble's 20th- Century Music Series had a regional look, a German evening on Tuesday attracting the smallest audience but perhaps the most exciting commission: a terse, dramatic Sextet by Detlev Muller-Siemens. Three days before, Per Norgard's rebarbative Scintillation and Poul Ruders' melodramatic The Bells, premiered by Lucy Shelton, gave very different impressions of the Scandinavian muse, framed by Stravinsky's Three Pieces for string quartet and Shostakovich's Seven Poems of Alexander Blok.

Christian Lindberg made light work of Schnittke's Dialog for trombone and ensemble - a blast of Sixties austerity - in an already severe setting. But it's not the Nash's way to do things by halves. In addition to the Strauss Prelude to Capriccio, the series ended with Berg's Adagio from the Chamber Concerto in the violin, clarinet and piano version, and Schoenberg's Suite, Op 6. Who else offers this repertoire as if it were just that - standard fare?