The National Youth Jazz Orchestra performs a different role to other art ensembles that bear the imprimatur of youth. Great names have risen through its ranks and some of its recordings are of a very high standard. So great expectations accompany a NYJO gig, and it's easy to forget that it is a group of talented but young musicians who should not be judged by the same criteria as other bands who take to the stage at the fabled Frith Street premises.

There have been incarn-ations of NYJO which have held their own with other professional outfits, despite the occasional rough edge. It is not being unkind to say that on the evidence of the first set on their first night, this is not one of them. There were too many nerves on show, too many palpable changes of gear between tutti and solo sections, the saxes lacked the silky confidence a line of shining horns should project, and many of the solos showed promise but were faltering.

All that said, the last number of the first set showed what this band can do. The winner of last year's Perrier Awards, the pianist Gwilym Simcock, took time out from sitting in on French horn and directed NYJO in his own arrangement of a Greek Cypriot dance. This was a chart worthy of the Buddy Rich big band, with all the complexity, changes of feel, use of dynamics and sheer excitement that that legendarily demanding drummer required.

Simcock really knows how to direct a big band, too. It's not always an easy task. Pianist leaders often walk away from their instrument to conduct the final note, a gesture just as well accomplished from the piano but done in front for show. The director of one band used to communicate his desires by clenching his fists as though he was about to bang on a table. At times, especially during solos, big band conductors simply have nothing to do, and have to find a way of occupying the space on stage without looking awkward. Simcock was comfortable with his place. He signalled ensemble passages to the relevant sections, and gave clear, authoritative direction that allowed NYJO to sing, scream and generally tear this cracking chart apart. Bill Ashton, NYJO's founder and longtime director, looked on fondly and proudly as Simcock took his place on the stand. He was right to do so. Sometimes NYJO produces one stunning player. At Ronnie's it featured an arranger and director who deserves the same description.