Acoustical analyses of Lombard speech by different background noise levels for tendencies of intelligibility

This study investigates acoustic variations when producing Lombard speech under the effect of a changing environment to identify adaptive tendencies of intelligibility. Analyses of the acoustic features of duration, F0, formants, spectral tilts and modulation spectrum in a dataset of speech at noise levels of - ∞, 66, 72, 78, 84, and 90 dB were carried out. The results show that the recognized tendencies (neutral-Lombard distinction), including lengthening vowel duration, increasing F0, shifting F1 and decreasing spectral tilts (A1-A3) are preserved among Lombard speech produced in backgrounds with a various noise levels. Our new findings are an abrupt change in F0 at 84 dB, increasing formant amplitudes, and H1-H2 variation, and a raised modulation spectrum. On the basis of physiological and psychological knowledge, we can give reasons for their correlations with intelligibility. Moreover, these variations continuously vary with increasing noise level. As a result, it is suggested that they are related to the adaptive tendencies of intelligibility