A real-time and gesture controlled voice synthesis software is applied to edutainment in the field of voice pedagogy. The main goals are teaching how voice works and what makes the differences between voices in an interactive, real-time and audio-visual perspective. The project is based on "Cantor Digitalis", a singing vowel digital instrument, featuring an improved formant synthesizer controlled by a stylus and touch graphic tablet. Demonstrated in various pedagogical situations, this application allows for simple and interactive explanation of difficult and/or abstract voice related phenomena, such as source-filter theory, vocal formants, effect of the vocal tract size, voice categories, voice source parameters, intonation and articulation, etc. This is achieved by systematic and interactive listening and playing with the sound of a virtual voice, related to the hand motions and dynamics on the tablet.