Lombard effect in Algerian Dialect Speech: Investigation of boosting and bypass strategies in narrowband noisy environment

Abstract

The paper presents the first investigation on the Lombard effect (LE) in the Algerian Dialect (AD) speech. It is devoted to the examination of boosting and bypass strategies in narrowband noisy environments (0.49–6.8 kHz). Speakers who adopt the boosting tactic would attempt to improve their audibility in noise by increasing the global intensity (I), the local intensity, and the duration (D) of their speech. The boost of the local intensity consists in amplifying the spectral magnitude of the speech waveform in the frequency region wherein the masking noise is beyond 55 dB. However, speakers who apply the bypass strategy would raise their speech in noise so that their fundamental frequency (F0) and first Formant (F1) will decrease. We built the AD Lombard Speech Corpus (ADLSC) that consists of continuous speech files uttered by eight native speakers in quiet and noisy conditions. The corpus contains phonetically rich words that cover all AD phonemes. To examine these strategies, we assessed the change in I, D, F0 and F1 from quiet to noisy environments. Subsequently, we evaluated the change in the local intensity via the computation of the Power Spectrum Ratio (PSR). Statistical tests were conducted to confirm the significance of the acoustic analysis. We found out that speakers raised their vocal effort in I and D. Furthermore, the measured PSRs confirmed the evidence that LE is frequency-specific in humans. Similarly, we noticed that speakers increased their F0 and F1 in noisy conditions. The results we obtained confirmed the boosting strategy but denied the bypass tactic. We compared our findings with the results reported in the state-of-the-art studies. The comparison revealed that LE in narrowband does not exhibit the same acoustic variations in AD and English.