Perspectives on wanted and unwanted sounds in outdoor environments : Studies of masking, stress recovery, and speech intelligibility

Abstract: An acoustic environment contains sounds from various sound sources, some generally perceived as wanted, others as unwanted. This thesis examines the effects of wanted and unwanted sounds in acoustic environments, with regard to masking, stress recovery, and speech intelligibility.In urban settings, masking of unwanted sounds by sounds from water structures has been suggested as a way to improve the acoustic environment. However, Study I showed that the unwanted (road traffic) sound was better at masking the wanted (water) sound than vice versa, thus indicating that masking of unwanted sounds with sounds from water structures may prove difficult. Also, predictions by a partial loudness model of the auditory periphery overestimated the effect of masking, indicating that centrally located informational masking processes contribute to the effect. Some environments have also been shown to impair stress recovery; however studies using only auditory stimuli is lacking. Study II showed that a wanted (nature) sound improve stress recovery compared to unwanted (road traffic, ambient) sounds. This suggests that the acoustic environment influences stress recovery and that wanted sounds may facilitate stress recovery compared to unwanted sounds. An additional effect of unwanted sounds is impeded speech communication, commonly measured with speech intelligibility models. Study III showed that speech intelligibility starts to be negatively affected when the unwanted (aircraft sound) masker have equal or higher sound pressure level as the speech sound. Three models of speech intelligibility (speech intelligibility index, partial loudness and signal–to–noise ratio) predicted this effect well, with a slight disadvantage for the signal–to–noise ratio model. Together, Study I and III suggests that the partial loudness model is useful for determining effects of wanted and unwanted sounds in outdoor acoustic environments where variations in sound pressure level are large. But, in environments with large variations in other sound characteristics, models containing predictions of central processes would likely produce better results.The thesis concludes that wanted and unwanted characteristics of sounds in acoustic environments affect masking, stress recovery, and speech intelligibility, and that auditory perception models can predict these effects.