Plenty of musicians improvise, but few do it quite like Trimpin. Midway through Peter Esmond`s documentary Trimpin: The Sound Of Ivention, the German-born engineer and composer is in his workshop, cleaning a glass tube for use in a gallery installation. As he polishes the tube with a cloth, it suddenly emits a high-pitched squeak. Trimpin`s ears prick up. He looks around, then tries rubbing the rube again. It squeaks again. He grins, and his knees buckle slightly with deligh. Trimpin licks a figer, rubs the end of the rube like you might a wine glass, and a sustained note sings out. A minute later, we are shown these tubes hanging in an exhibition, their sounds triggered by electronic valves hooked up to a computer.