Individual monitoring of hearing status: Development and validation of advanced techniques to measure otoacoustic emissions in suboptimal test conditions

Abstract

Scientific evidence suggests that measurement of otoacoustic emissions (OAE) is a reliable tool to detect the early onset of noise induced hearing loss. Nevertheless, the individual field measurement of otoacoustic emissions on industrial workers is very challenging in practice because the high level of ambient noise usually disturbs the OAE measurement. The use of OAE measurement probes with high passive noise isolation allows the attenuation of most of the high frequency ambient noise, but it is often insufficient for the low frequency content of the ambient noise. In the described research, a new type of OAE system, suitable for the continuous monitoring of OAE levels on an individual worker, has been designed as a pair of earpieces each featuring an external microphone, an internal microphone and a pair of miniature receivers. Adaptive noise reduction (ANR) processing the measured distortion product OAE (DPOAE) is used to further improve the Signal-to-Noise ratio in frequencies mostly where passive isolation remains insufficient. The ANR technique relies on a Normalized Least-Mean-Square (NLMS) algorithm that uses the ipsilateral external microphone and the contralateral internal microphone to denoise the measured DPOAE signals for each in-ear OAE probe. A side-by-side comparison with commercially available clinical OAE equipment on 8 test-subjects successfully confirmed that the developed OAE system would be suitable for the continuous monitoring of workers' hearing capabilities in industrial noise environments with levels up to 75 dB(A).

On the potential for artificial bandwidth extension of bone and tissue conducted speech: a mutual information study

“…The transfer function between the OEM and IEM is calculated to remain as close as possible to realistic conditions. This is achieved by playing white noise over loudspeakers in the audiometric booth while the speaker is still equipped with the in-ear HPD [13]. The noise signals collected by the IEM and OEM are then used to calculate the transfer function between the two microphones, i.e.…”

Development, validation and application of a generator for distortion product otoacoustic emissions

“…The artificial generator therefore has to be regarded as representative for a single individual drawn from the population. The DPOAE generator can support the development of hardware and software solutions that allow extending the range of tolerable background noise levels [7]. This would enabling robust DPOAE acquisition in even harsher measurement environments.…”

“…This example shows that improvements in OAE equipment can have a substantial influence on the final DPOAE amplitudes. This is also important outside routine clinical conditions, where constantly advancements are being made to enable DPOAE acquisition in suboptimal test conditions [7,27,28].…”

“…This is essential as the DPOAEs are becoming an objective, fast and reliable way to detect early signs of noise-induced changes in hearing sensitivity [7,8] and a tool for direct monitoring of the efficiency of hearing protection [7,8].…”

“…However, the field of application of OAE measurements is currently expanding. As an example, OAE measurements are also suggested as a tool for early detection of occupational and/or recreation noise-induced hearing damage, or for indirect monitoring of real exposure under hearing protector [7,8]. New devices are being developed to withstand the difficult measurement conditions that might occur outside the clinical environment.…”