Perceptual analysis of the speech intelligibility and soundscape of multilingual environments

This paper examines the perceived speech intelligibility of English, Polish, Arabic, and Mandarin and, more generally, the soundscape associated to multilingual environments. Listening tests were used to evaluate three acoustic environments (an airport, a hospital, and a café) under three room acoustic conditions defined by a different speech transmission index (STI) (STI=0.4, 0.5 and 0.6). In the tests, participants rated eleven semantic attributes representative of speech perception and the overall soundscape (speech intelligibility, speech level, speech pleasantness, noisiness, annoyance, relaxation, comfort, environment pleasantness, eventfulness, excitement, and familiarity). Results obtained indicate that inter-language comparisons based on perceived speech intelligibility are different from those obtained from objective speech intelligibility tests. Noticeably, English participants were found to be most sensitive to changes in room acoustic conditions and to meaningful and distractive noise sources, whilst Arab participants were least sensitive to changes in room acoustic conditions and more tolerant to noise. Perceived speech intelligibility correlated significantly with non-acoustical factors (speech pleasantness, comfort and environment pleasantness), and ‘emotional factors’ (annoyance, relaxation, comfort and environment pleasantness) explained a large portion of the variance in soundscape assessment. Results also showed that language affected the perceived speech intelligibility marginally (p = 0.051) and noisiness significantly (p = 0.047), the latter being the best indicator of cultural variations amongst the attributes tested. Overall, the study shows that designing for speech intelligibility cannot be solely based on room acoustic parameters, especially in the case of multi-lingual environments.