RESUMO
The ISO 3382-3 (2022) standard defines single number quantities (SNQs) characterizing the spatial decay of speech (D2S, LpAS4m, rC) and of its intelligibility (rD). The standard assesses the accuracy of the measurement using a unique uncertainty value for each SNQ, relying on a round-robin test performed in a single office. To make this assessment more accurate, analytical expressions have been established by applying the law of propagation of uncertainty. These expressions, although precise, are too complex to be included in the standard. This work consists of their simplification, relying on 95 measurements conducted in 36 companies in France and Germany. First, the terms associated with distance measurement uncertainties were found to be negligible. Second, the estimation of the uncertainties of A-weighted speech levels and Speech Transmission Index, based on the measurements made at the workstations constituting the 95 paths, enabled further simplifications. Finally, simplified expressions turn out to be as accurate as the original expressions, and the estimated uncertainties are comparable to those reported by Yadav et al. (2019). If a unique value of uncertainty is to be retained for each SNQ, this study suggests 0.6 dB for D2S and LpAS4m, 7% for rC, and 10% for rD.
RESUMO
Objective: Hearing aids are more and more technically advanced, but do not necessarily guarantee the reproduction of useful signals in all working environments. This is particularly the case for speech intelligibility. This study focuses on the prediction of hearing aid performance in the case of a moderate deafness setting, in service and industrial work environments. To improve intelligibility, hearing aids propose signal processing options such as noise reduction and compression. These processes can transform hearing aids into nonlinear systems. The aim of this study is to develop a nonlinear method for the characterization of hearing aids. Materials and Methods: The method is based on the synchronized swept sine (SSS) signal method.[16] The SSS method is applied for determining hearing aid frequency responses fitted according to the present methodology and several processing options. The characterization of hearing aid's program containing the noise reduction function is specifically analyzed. Indeed, to be fully active and efficient, the hearing aid, with the noise reduction feature activated, needs to be immersed in a noisy environment which does not allow nonlinear characterization. A linear approach is taken to study this feature. Three hearing aids commonly sold by hearing care professionals are studied here; all of them have three different programs. The characterization for each program is discussed. Results: The statistical study showed that the intelligibility, assessed using the speech transmission index in these sound environments, is well estimated for every program, although certain differences are observed when the compression effect is too high in the service work sector. Conclusion: The characterizations of hearing aids using the programs studied did not highlight the presence of frequency nonlinearities. The characterization method could not take into account amplitude nonlinearities when there is too much gain compression in the hearing process. Globally, all the hearing aid programs provided a very significant improvement in intelligibility in service and industrial work contexts.
