The reactable, is a state-of-the-art multi-user electro-acoustic music instrument with a tabletop tangible user interfacedeveloped by Universitat Pompeu Fabra in Barcelona. Several simultaneous performers share complete control over the instrument by moving physical artefacts on the table surface and constructing different audio topologies in a kind of tangible modular synthesizer or graspable flow-controlled programming language.The reactable hardware is based on a translucent round table. A video camera situated beneath, continuously analyzes the table surface, tracking the nature, position and orientation of the objects that are distributed on its surface, representing the components of a classic modular synthesizer. These objects are passive without any sensors or actuators, users interact by moving them, changing their position, their orientation or their faces (in the case of volumetric objects).
