Noise annoyance and application of the Harmonica index at short time intervals

The Harmonica index (HRM) is aimed to quantify the perceived noisiness of environmental sounds on an hourly basis by a score on a linear scale from quiet to very noisy. The index is computed as the sum of the background noise (BGN) and the sound events (EVT) emerging from BGN and has been developed to facilitate communication with the public and to help local authorities in the decision-making process. In this paper, the HRM index has been applied to short time intervals, providing an increase in the time resolution of sound level acquisition from 1 s to 0.1 s. Six sound recordings were considered, taken in different urban contexts (i.e., parks, road traffic noise, construction sites), each lasting two minutes and divided into four sequential soundtracks of 30 s each. The tracks were played back randomly in laboratory listening tests to collect ratings of perceived annoyance given by participants after each soundtrack and, at the end of the four soundtrack sequences, the annoyance rating of the whole sound. The results show that the short-time application of the index is sensitive to the qualitative characteristics of the background and events, and needs improving before being used.