THE brilliance lay in the simplicity of the concept.

The Scottish Ensemble's December touring programme, at Oran Mor on Tuesday and entitled Variations, enshrined a fundamental musical principle. Take a basic musical idea – it might be on top, as a melody, or it might be underneath, as a bass line – and vary it to develop an entire piece from and around that common material. For centuries composers have feasted on the concept.

Martin Suckling, in his new piece with the quirky title, Mr Jonathan Morton, His Ground – Postcard 2, premiered on Monday, turned the concept of variation inside out.

Around the basic musical line, demonstrated by Scottish Ensemble leader Jonathan Morton before performance, Suckling wove decorative clouds, which may have been modernistic in colouring, but were expressionistic in essence. It was written with assurance and conciseness, made its point, and was gone. A perfect construction.

Benjamin Britten's Frank Bridge Variations, on the other hand, though a hugely-effective concert piece (stunningly played in the full-on acoustic of Oran Mor), seems to me to flag at its mid-point, almost as though the young Britten fired his best shots, notably in the Waltz and Aria Italiana, rather prematurely.

Prince of the night was the performance of Bach's Goldberg Variations, perfection in music and in variation form, in its arrangement for strings by Dmitry Sitkovetsky. With their light, historically-informed performance, Morton's group sagely and characterfully brought a quintessentially-keyboard piece off the page and into expressive life.