Topological invariants for substitution tilings and their associated $C^\ast$-algebras

A color organ device for producing a visual display of lights responsive to electrical signals produced on respective channels of a four-channel stereo. The device includes a housing having a plurality of banks of lights therein which is rotated by an electric motor. A interpreter is provided for selectively separating the frequencies produced by the four-channel stereo for selectively energizing the banks of lights. Slip-rings are provided for making electrical contact between respective frequency discriminating circuits and the banks of lights.