reactable

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„reactable“

reactable in use with seven tangibles placed to control seven synth modules

reactable in fully lit room. One tangible is placed in the active area, with others on the inactive periphery. On the right is a cube tangible with fiducials visible on two of its sides.

The reactable is an electro-acoustic music 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.^[1]

1 Basic operation
2 Structure
3 reacTIVision
4 Presentations
5 See also
6 References
7 External links

[edit] Basic operation

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.

[edit] Tangibles

There are various types of tangibles representing different modules of an analog sythesizer. 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 limits a VCO to the notes of a musical scale.

[edit] Using tangibles with the display

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.

[edit] Example of operation

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.

Placing a filter tangible between the VCO and the output causes the VCO's waveform to connect to the filter, and the filter waveform to connect to the output. If an LFO tangible is placed near the VCO, a waveform will then appear connecting those two, and the LFO will modulate the VCO.

[edit] Structure

The reactable's main user interface consists of a translucent table. Underneath the table is a video camera, aimed at the underside of the table and inputing video to a personal computer. There is also a video projector under the table, also connected to the computer, projecting video onto the underside of the table top that can be seen from the upper side as well.

Placed onto the table are the tangibles that have fiducials attached to their underside which are seen through the table by the camera. Fiducials are printed black and white images, consisting of circles and dots in varying patterns, optimized for use by reacTIVision. reacTIVision then uses the fiducials to understand the function of a particular tangible.

Most of the tangibles are flat, with one fiducial on the underside. Some other tangibles are cubes, with fiducials attached to several sides, allowing those tangibles to serve multiple functions.

[edit] reacTIVision

The video received from the video camera into the computer is processed by open-source computer vision software called reacTIVision originally developed by Ross Bencina and Martin Kaltenbrunner. reacTIVision detects cartesian and rotational placement of fiducials in video images, then outputs OpenSound Control messages for music synthesizer software, either using MIDI or a specially designed packet based network protocol TUIO. reacTivision also tracks fingertip placement.

reacTIVision also communicates to the TUI software that outputs to the video projector.

[edit] Presentations

The reactable has been presented and performed with at various festivals and conferences such as Ars Electronica, Sónar, NIME and SIGGRAPH.

Icelandic songstress Björk is perhaps the first musician outside of the select presentations and demonstrations to use a reacTable in live performance. Björk's 2007 world tour supporting her 2007 release Volta use the instrument in several songs including "Declare Independence"; Björk's live inaugural use of the instrument took place at the Coachella Valley Music and Arts Festival on April 27, 2007.