The cognitive processes behind human bimodal (audio visual) perception are not well understood. This contribution presents an approach to reach a deeper understanding by means of subjective assessments of (interactive) audio visual applications. A tool developed for performing these assessments is introduced, and the audio rendering system design of that tool is explained: its modular character, the signal processing flow as well as the possible reproduction setups are discussed. Finally, an example for the assessment of geometrically based room simulation and preliminary test results are given.