Conceiving digital musical instruments might be challenging in terms of spectator accessibility. Depending on the interface and the complexity of the software used as a transition between the controller and sound, a musician performance can be totally opaque for the audience and loose its interest. This paper examines the possibility of adding a visual feedback to help the public understanding, and add expressivity to the performance. It explores the various mapping organizations between controller and sound, giving different spaces of representation for the visual feedback. It can be either an amplification of the controller parameters, or a representation of the related musical parameters. Different examples of visualization are presented and evaluated, taking the Cantor Digitalis as a support. It appears the representation of musical parameters, little used compared to the representation of controllers, received a good opinion from the audience, highlighting the musical intention of the performers.