Methods for the evaluation of warning sounds perception: the influence of hearing impairment and hearing protector

In noisy industrial workplaces, the perception of warning sounds is crucial to ensure the safety of the workers. On the ground, the perception of warning sounds not only depends on the levels and spectra of the warning signal and of the ambient noise. It also depends on other parameters such as the hearing status of the workers (hearing loss and frequency selectivity) and, when a hearing protection device is worn, the spectral distribution of its attenuation.
In order to assess, in a given ambient noise, the minimum level required for a warning signal to be heard, two complementary approaches are used. The first approach is subjective. It consists, via listening tests, in measuring the signal detection thresholds (determination of the psychometric function using the method of constant stimuli). The second approach is objective. It consists in calculating the masked thresholds using a psychoacoustic model. The use of such a model makes it possible to study, both separately and in combination, the effects of the different parameters that may affect the signal perception.
As part of a collaboration with SNCF and « Agence d’Essai Ferroviaire », the results given by these two approaches are compared for several transportation noise situations and for different types of hearing protectors.
These results will be complemented by auditory simulations. Audio signals will be first modified in order to reproduce the effects of the different parameters (hearing protector attenuations and hearing impairments). Then they will be used as auditory stimuli in listening tests. Based on these auditory simulations, the objective is to be able to choose the most appropriate hearing protector using comparative listening, or to validate this choice by also taking into account the effects of the hearing impairment of an individual.