Gather Round the reacTable

Most musical instruments, electronic or otherwise, are designed to be played by one person. If you bring several individuals and their instruments together,
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FIG. 1: The reacTable is played by placing and moving specially designed objects that represent synthesis modules on a translucent tabletop. Connections between modules are made dynamically and are represented by waveforms and other shapes.

Most musical instruments, electronic or otherwise, are designed to be played by one person. If you bring several individuals and their instruments together, you have an ensemble. But what if you could turn that paradigm around by bringing several people together to play a single instrument, collaborating on the final audio outcome?

That's exactly the idea behind the reacTable, a research project being conducted by the Music Technology Group at the Universitat Pompeu Fabra ( in Barcelona, Spain. The reacTable is a computer-based musical instrument that was designed to be played by several people simultaneously.

As its name suggests, the reacTable's basic form is a table — a structure around which people traditionally gather to converse and collaborate. In this case, the tabletop is round (to allow all participants equal access) and made of translucent plastic. Under the table is a video camera that senses the position, shape, and orientation of specially designed objects placed on the surface. This information is used by a computer to generate visual images on the table with a projector below the surface and audio signals from a software-based synthesizer.

The sound engine was inspired by modular synthesizers, such as those from Moog and Buchla, and object-oriented musical environments, such as Max/MSP and Pure Data. Different objects on the table represent different synthesis modules, such as sound generators, modulators, controllers, sequencers, and mixers. Connections between the modules are represented graphically on the table by images of audio and modulation waveforms, among other shapes (see Fig. 1). Even more interesting, the connections are made automatically and dynamically, based on the modules' functions and their proximity to each other.

The first reacTables are about one meter in diameter, allowing as many as four people to participate in a performance. As each person places modules on the table and moves them around, the connections between them change, creating an ever-evolving soundscape. In addition, turning a module in place varies an associated parameter, much like turning a knob on a hardware synth.

To involve more people, multiple reacTables can be networked together, with the icons of modules on each surface appearing on all of them. They can also be networked over the Internet; in fact, one of the first performances included one reacTable in Barcelona and another one in Linz, Austria. Participants at one table can't directly affect the modules on another table, but the modules from all tables combine to create the final sound, which all participants hear. Each reacTable has its own audio system, and only control signals are transmitted over the network, minimizing latency.

The video camera scans the tabletop in real time, and its signal is analyzed by a program called reacTIVision. The resulting data goes to a connection manager, whose job is to establish the connections between modules. This information, along with the type, location, and orientation of each module, is sent to a visual synthesizer (which controls the projector) and to the audio synthesizer. Waveforms from the audio synth are also sent to the projection system to be rendered on the table surface.

The reacTable was conceived to serve a wide variety of purposes. For example, it can be part of an interactive exhibit for untrained visitors to play with. It can also be used as a sophisticated instrument by skilled musicians in a concert setting. One particularly fascinating aspect of the device is that it merges the processes of building and playing a musical instrument into a single activity, which opens new creative vistas for all who want to expand their musical horizons.