Time-varying voice directivity in real-time room acoustic simulation: Implementation and perceptual evaluation

Source directivity is an integral part of room acoustic simulation, affecting not only the intensity and frequency balance of the direct sound depending on source orientation, but also room-acoustic parameters, such as the direct-to-reverberant energy ratio. While the directivity of a loudspeaker is time-invariant, the directivity of other sound sources, such as the human voice, varies over time. Whether these time-dependent directivity changes must be fully considered for a plausible binaural rendering of speech remains an open question, requiring rendering solutions that can reproduce time-varying directivity. This work provides three key contributions. First, it introduces a feature for liveRAZR—a real-time, six-degrees-of-freedom room acoustic simulator—to render sound sources with time-varying directivity from Ambisonics input. Second, it proposes a method to generate speech material with time-varying directivity from monaural recordings using phoneme-dependent directivity filters. Third, it presents a listening experiment comparing fluent speech with multiple time-varying and static directivities regarding transfer-plausibility and perceptual qualities. Time-varying directivity did not significantly improve transfer-plausibility or liveliness and source-orientation clarity ratings compared to static, measurement-based directivity in the tested scenario. However, analytically obtained spherical head model directivity reduced these perceptual qualities, indicating that measurement-based voice directivity is preferable for demanding immersive extended reality applications.