Vincent Nadon

Use of passive hearing protectors and adaptive noise reduction for field recording of otoacoustic emissions in industrial noise

Distortion product otoacoustic emissions (DPOAEs) can detect noise-induced hearing loss in-field, but their data extraction is very sensitive to background noise. This paper investigates how passive and active noise reduction enhance DPOAE recording based on data collected in white noise from 54 dB(A) to 90 dB(A). Despite considerable high-frequency attenuation from a proper placed DPOAE probe, 54 dB(A) background noise deteriorates the test outcome substantially. More low-frequency attenuation by an extra passive earmuff enables measurements in white noise levels of 70 dB(A). The relationship between external sound level and noise recorded by the DPOAE system has been statistically modeled. Additionally, the upper limits of attenuation improvement are analyzed by quantifying residual physiological noise. Furthermore, for an earplug integrating microphone and speakers of the DPOAE measurement probe, adaptive noise reduction processing on the DPOAE signal is used to improve the signal-to-noise ratio. The a...

Field monitoring of otoacoustic emissions during noise exposure: Pilot study in controlled environment

Purpose In spite of all the efforts to implement workplace hearing conservation programs, noise-induced hearing loss remains the leading cause of disability for North American workers. Nonetheless, an individuals susceptibility to noise-induced hearing loss can be estimated by monitoring changes in hearing status in relation to the level of ambient noise exposure. The purpose of this study was to validate an approach that could improve workplace hearing conservation practices. The approach was developed using a portable and robust system designed for noisy environments and consisted of taking continuous measurements with high temporal resolution of the health status of the inner ear using otoacoustic emissions (OAEs). Method A pilot study was conducted in a laboratory, exposing human subjects to industrial noise recordings at realistic levels. In parallel, OAEs were measured periodically using the designed OAE system as well as with a commercially available OAE system, used as a reference. Results Variations in OAE levels were analyzed and discussed along with the limitations of the reference and designed systems. Conclusions This study demonstrates that the monitoring of an individuals OAEs could be useful in monitoring temporary changes in hearing status induced by exposure to ambient noise and could be considered as a new tool for effective hearing conservation programs in the workplace.

Design considerations for robust noise rejection in otoacoustic emissions measured in-field using adaptive filtering

Otoacoustic emission (OAE) measurement is a sensitive and effective technique to monitor changes in the inner ear potentially induced by noise exposure. However, outside a controlled testing environment, measurements are challenging since the level of ambient noise might be higher than the low-level OAE response. Therefore, an OAE system was designed, suitable to measure OAEs repeatedly on an individual worker in noisy test conditions. This system features a left and right earpiece, each equipped with a pair of miniature loudspeakers, an external and an internal microphone. In addition to the passive attenuation of the earpiece, adaptive filtering on the distortion product OAE (DPOAE) signals is used to further enhance the ratio between the measured OAE signal and interfering noise. The adaptive filtering technique uses the sound captured by the ipsilateral external and internal microphones as well as from the contralateral internal and external microphones. In this paper, the accuracy of DPOAE signals are studied using different combinations of the four microphones in single and dual adaptive filter topologies, as well as the benefits of adding a fixed transfer function in the adaptive filtering algorithm topology to estimate the acoustic path. Side-by-side comparison shows that a dual-stage adaptive filtering algorithm, using a combination of the contralateral internal microphone with the ipsilateral external microphone, is the most promising approach to denoise the DPOAE signal.

Effects of noise exposure on hearing health evaluated through short interval otoacoustic emission monitoring: Preliminary results with low and moderate noise exposure groups

Industrial workers are often exposed on a daily basis to noise doses that put them at risk of Noise-Induced Hearing Loss (NIHL), which remains the largest cause of indemnity in North America industries. To improve occupational hearing loss prevention programs, a method to continuously measure hearing fatigue using otoacoustic emissions (OAE) has already been proposed by the authors using a portable and robust OAE system designed for noisy industrial use. The effectiveness in the field of the aforementioned method is examined by comparing a control group of unexposed subjects in laboratory and noise exposed subjects in the field. All participants are equipped with an hearing protection earpiece which includes the usual OAE measurement components as well as a microphone mounted on the outer faceplate of the earpiece. At regular intervals over the course of the day, the growth function of distortion product OAEs is measured for both groups while simultaneously measuring noise levels inside and outside the ea...

Real-time estimation of the passive attenuation for otoacoustic emission measurement probes

Despite hearing loss prevention programs in place at work, noise-induced hearing loss (NIHL) remains the first reported occupational disease. To improve the detection of over-exposure to noise, an initial proof-of-concept for field monitoring of inner-ear health using otoacoustic emissions (OAE) was developed and successfully validated in laboratory conditions. However, in real-life situations, the unsupervised placement of the OAE probes remains a challenge: proper fit of the probe in the ear canal is required to ensure adequate hearing protection of the wearer, to improve the signal-to-noise ratio of OAE measurements and to maintain the proper calibration of stimuli signals in the case of the Distortion Product OAE (DPOAE) approach used. Algorithms were recently developed to quantify, in real-time, from the OAE probe microphones and receivers signals, the passive attenuation of the OAE probes. The validation of this approach was conducted, in laboratory conditions, on five human subjects exposed to indu...