Created by Felicie Bazelaire, CoO is a string ensemble drawn from the French new music ensemble ONCEIM; CoO develops new repertoire for strings, collaborating with composers like Bertrand Denzler, who wrote this innovative composition "Arc" in two parts, a work applying unusual techniques to bowed strings, particularly lower bass tones, for fascinating results.

This duo arose from the meeting between two violists avid to confront with their instrumental double to create a common sound universe from the same instrument played by two different personalities.