Distortion in Tone Production due to the Lombard Effect

This study investigates the Lombard effect triggered at different noise levels on the F0 contours of tones in Northern Vietnamese. We hypothesize that due to the human talkers’ limited capacity for hyper-articulation, the dynamic range of the F0 contours may be decreased, potentially resulting in a reduced distinction between lexical tones. For example, for rising tones, the slopes of the overall F0 contours might be flattened at higher noise levels if the demand for hyper-articulation forces elevation of the F0 contours to an unsustainable level. Acoustic analyses of speech produced in quiet and two noise levels confirmed that the F0 contours are raised across all lexical tones and talkers in noise and the dynamic range of the F0 contours decreased for tone C2. The results broadly supported the hypotheses that hyper-articulation due to the Lombard effect may cause tone distortion. The present findings are promising and invite further research into whether tone confusion is experienced by human listeners.