Effects of source identifiability on loudness and annoyance

A pervasive problem in sound-quality evaluation is whether observers actually judge the sound (e.g. a low-frequency rumble), or the source (e.g. the factory across the street). Very often, it is desirable to disentangle these two aspects to get separate readings, e.g. of the sensory and emotional impact of sound. In an initial study, a signal-processing scheme developed by a collaborator at the Technical University of Munich has been used to render a number of environmental sounds unidentifyable while preserving their loudness-time functions. To apply this methodology to a stimulus set covering a larger range on the loudness continuum, first a wide range of environmental noises including various product sounds was recorded. A pilot study was performed to select sounds that are highly identifiable in their original version. In the first part of the main experiment, four independent groups of subjects (N = 25 each) responded on category-subdivision scales of loudness or annoyance to either the original or processed version of the selected signals. In the second part, subjects provided ratings of the stimuli on a Semantic Differential. Data analyses included the specification of the impact of source identifiability on loudness and annoyance judgements as well as an investigation of these effects in terms of differences in the semantic profiles elicited by the sounds. (Center contract).