ReacTable

The Reactable is an electronic musical instrument with a tabletop Tangible User Interface that has been developed within the Music Technology Group at the Universitat Pompeu Fabra in Barcelona, Spain by Sergi Jordà, Marcos Alonso, Martin Kaltenbrunner and Günter Geiger.

In late 2010, a mobile version of the Reactable was released for iOS.

The Reactable is a round translucent table, used in a darkened room, and appears as a backlit display. By placing blocks called tangibles on the table, and interfacing with the visual display via the tangibles or fingertips, a virtual modular synthesizer is operated, creating music or sound effects.

There are various types of tangibles representing different modules of an analog synthesizer. Audio frequency VCOs, LFOs, VCFs, and sequencers are some of the commonly used tangibles. There are also tangibles that affect other modules: one called radar is a periodic trigger, and another called tonalizer limits a VCO to the notes of a musical scale.

The table itself is the display. As a tangible is placed on the table, various animated symbols appear, such as waveforms, circles, circular grids, or sweeping lines. Some symbols merely show what the particular tangible is doing, others can be used by fingertip to control the respective module.

If a VCO tangible is placed on the table, a VCO module is added to the virtual synthesizer. In the display, a waveform will appear between the tangible and the "output" (a bright spot at the center of the table), and a circle appears around the tangible which allows fingertip control of the amplitude of the waveform. Additionally, in this example the tangible can be rotated by hand to change the frequency.

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Wikipedia