The effect of the frequency energetic content of noise on the Lombard effect and speech intelligibility

The Lombard Effect is an increase in vocal effort in response to rising noise levels and disturbance in the communication environment. The objective of this study is to evaluate the Lombard Effect during four intensity levels from 45dBA to 75dBA of low-frequency, medium- frequency, and high-frequency energy noise to measure the effect of disturbance and vocal discomfort on the speaker’s intent to communicate, as well as the effect on speech intelligibility. Twelve conditions were randomly presented and recorded for each participant with the three types of noise and levels. At each condition, 20 participants were asked to read a passage. Immediately following each reading, participants were asked to rate the amount of noise disturbance and vocal comfort they had experienced. After, the speech intelligibility was evaluated by asking the participants to repeat the sentences of the QuickSin test emitted by a Head and Torso Simulator. The medium-frequency energy noise showed the highest Lombard Effect and the stronger decrease in intelligibility. In the conditions with noise with mid-frequency energetic content, the decrease in intelligibility was drastic with the increase in noise level. Low-frequency noises minimally impact speech intelligibility. High-frequency noises show little change in intelligibility with the increase in noise level.