Late on Friday night at WOMAD, on the more intimate Charlie Gillett Stage in Charlton Park, there was an unusual cross-cultural treat. Ballaké Sissoko is one of Mali’s most accomplished kora players: not as well known as his Bamako next-door neighbour Toumani Diabaté and more firmly rooted in Manding musical tradition, but undoubtedly in the same class. Vincent Ségal is a brilliant French cellist who moves with consummate ease from the classical repertoire to free jazz. They are both technical virtuosi but neither of them plays to the gallery.