Design and evaluation of a human-in-the-loop Lombard effect simulator

Abstract

When multiple people converse in an indoor environment, achieving satisfactory communication is often challenging due to high level noise caused by poor acoustic design. Communication in noisy environments gives rise to the Lombard effect, an involuntary reflex that causes one to raise their voice in the presence of noise. This may produce more intelligible speech for listeners, but the increase in speaker sound level eventually contributes to the Cafe effect occurring in the environment. To control the tendency of noise build-up, it is of interest to investigate the Lombard e!ect under different acoustic conditions; however, it can be difficult to control variables in real environments, which may affect test repeatability. This study investigates if the Lombard effect can be simulated by replicating the dynamic changes in sound level of speakers in a real environment, and to what extent speakers change their voice level when immersed into the simulated environment. The study uses spatial sound reproduction to simulate environments with varying acoustics and examines speakers’ sound level when the build-up occurs. It will provide a novel method that allows controlled study of speakers’ behaviour in noisy environments and provides opportunity to investigate one speaker’s effect on the overall sound level within the simulated environment. The results observed show that participants performed similarly in terms of overall noise level and maximum measured voice level in different virtual acoustic environments. The Lombard effect between virtual environments shows no difference, contrasting with the expectation of rooms with a higher reverberation time causing a higher Lombard slope. The study requires further measurements to evaluate the simulator in terms of its accuracy to real environments.