Pleasantness evaluation of combined environmental sounds

Predicting human evaluation of complex acoustical environments still poses a challenge. In order to explain annoyance reactions to combined sounds, various models have been developed, often based on a weighted combination of loudness or sound pressure levels. However, these models are limited regarding the evaluation of sound quality and pleasantness. Natural sounds, for example, can also have a beneficial effect in noisy environments, although they represent additional sound sources, which increase the overall sound pressure level. Moreover, a superposition of different sounds can produce musical structures like rhythm patterns or harmonic constructs, which influence the evaluation as well. Behind this background, we investigated how pleasantness ratings of singular sounds affect the overall evaluation of their respective combinations. Since pleasantness judgements are often confounded with loudness, a listening experiment was conducted, to separate these two variables. A positively and a negatively perceived sound, each one with three different loudness levels, were combined in pairs in all possible configurations and evaluated by test participants. The results of this experiment were used to validate a linear regression model, which explains well the overall pleasantness evaluation of two combined environmental sounds, using the weighted sum of the singular pleasantness ratings and their interaction.