A practical approach to music theory on the Reactable

The Reactable is an electronic musical instrument with a tangible tabletop multiuser interface (Jordà et al., 2007) that’s been developed within the Music Technology Group at Universitat Pompeu Fabra in Barcelona, Spain.

It’s designed as an instrument to make users explore and create soundscapes in the least possible intimidating way, thus allowing the widest possible range of users to successfully experiment with sound from the first moment, no matter what age or musical education level they are.

This goal is achieved by presenting a user interface that adds sight to hearing and touch, thus combining audible and visual feedback to help users better understand and control what’s happening at any given moment. Arguably, addition of visual feedback is the key point that makes the Reactable sensibly easier to approach than any other instrument, whose in turn don’t usually present sound production and control in any different way than by hearing.

The Reactable is a round translucent table that appears as a backlit display with which users directly interact using some special objects and their finger tips. Under the surface it features a fairly complex system made of infrared lamps, mirrors, an infrared-sensitive high speed camera and a common vga beamer.

Infrared lamps illuminate the bottom of the translucent table surface, thus allowing “inactive” areas to be ignored while “active” ones – such as fingers and tangibles – reflect the light and are captured by the camera. The captured video stream is then processed by a computer using reactivision, which extracts descriptors of the various objects it can recognize, and stream them over the network1 to both the audio and visual synthesizers.

Both the synthesizers use the data sent by reactivision to produce audible and visual feedbacks. While sounds are simply played through a sound card, visual output is projected on the surface using the vga beamer that’s inside the table.