On the Lombard Effect Induced by Vehicle Interior Driving Noises, Regarding Sound Pressure Level and Long-Term Average Speech Spectrum

Journal article, 2012

In this paper, the influence of typically appearing interior driving noises on the production of speech inside vehicles is described. The automatic reflex of raising one’s voice in noisy environments, known as the Lombard Effect [1], is quantified both in the sound pressure level and in the long-term spectral distribution of read speech. For this purpose, a laboratory experiment with 30 participants was performed. In addition to a noise-free reference condition, driving noises at various sound pressure levels as well as noises with white and speech-like spectra were presented to the test attendees while reading out loud a written text. The effects of these different noises on the speech’s sound pressure level and spectral distribution were quantified. In conclusion, there is no significant impact of the noise shape on the spectral content of the respective speech, while the noise-affected speech is significantly different to speech under the quiet condition. In regard to the speech’s sound pressure level, an octave-band analysis of the background noises with a band weighting commonly used for speech intelligibility measurements is proposed to predict speech levels in the tested noise environments.