The effects of spectral fine structure and amplitude envelope on perceived similarity and identification of approaching vehicles

Abstract

The recognition and identification of important complex natural sound sources is a critical component of maintaining environmental awareness. The properties of sound sources are not static; environmental factors can cause dramatic shifts in acoustic structure. The present study investigates the effects of large imposed acoustic changes on listener perception of approaching ground and aerial vehicles. In the first experiment, listeners rated the perceived similarity of the vehicle stimuli that were either (1) unaltered, or had (2) spectral fine structure replaced with random noise, or (3) had their natural amplitude envelopes flattened. The results of a multidimensional scaling (MDS) analysis found that the ordering of perceptual space for each of the conditions was generally a function of the acoustic information available. The second experiment investigated listener identification for the same sets of sounds. Identification performance across vehicle sounds had good agreement with similarity mappings and was best when spectral fine structure was smoothed and variations in amplitude envelope were maintained, and worst when the opposite was true. These results are consistent with the notion that amplitude envelope is a critical component in the recognition and identification of complex natural sound sources.