Can we measure the impact of the presence of an audience on musicians' performances? By exploring both acoustic and motion features for performances in Immersive Virtual Environments (IVEs), this study highlights the impact of the presence of a virtual audience on both the performance and the perception of authenticity and emotional intensity by listeners. Gestures and sounds produced were impacted differently when musicians performed at different expressive intents. The social factor made features converge towards values related to a habitual way of playing regardless of the expressive intent. This could be due to musicians' habits to perform in a certain way in front of a crowd. On the listeners' side, when comparing different expressive conditions, only one congruent condition (projected expressive intent in front of an audience) boosted the participants' ratings for both authenticity and emotional intensity. At different values for kinetic energy and metrical centroid, stimuli recorded with an audience showed a different distribution of ratings, challenging the ecological validity of artificially created expressive intents. Finally, this study highlights the use of IVEs as a research tool and a training assistant for musicians who are eager to learn how to cope with their anxiety in front of an audience.