Wind noise at microphones within and across hearing aids at wind speeds below and above microphone saturation

Abstract

The variation of wind noise at hearing-aid microphones with wind speed, wind azimuth, and hearing-aid style was investigated. Comparisons were made across behind-the-ear (BTE) and completely-in-canal (CIC) devices, and between microphones within BTE devices. One CIC device and two BTE devices were placed on a Knowles Electronics Manikin for Acoustic Research. The smaller BTE device had vented plastic windshields around its microphone ports while the larger BTE device had none. The microphone output signals were digitally recorded in wind generated at 0, 3, 6, and 12 m/s at 8 wind azimuths. The microphone output signals were saturated at 12 m/s with wind-noise levels of up to 116 dB SPL at the microphone output. Wind-noise levels differed by up to 12 dB between microphones within the same BTE device, and across BTE devices by up to 6 or 8 dB for front or rear microphones, respectively. On average, wind-noise levels were lowest with the CIC device and highest at the rear microphone of the smaller BTE device. Engineering and clinical implications are discussed.

Microphone variability and degradation: implications for monitoring programs employing autonomous recording units

“…For example, for microphones at -41 dBV, the addition of 8 dBA of white noise (from Beaufort 2 to Beaufort 3 conditions) reduced the effective detection area of loud calls by 19-58% and 64-72% across the quiet species. Past research suggests that wind affects detection of calls in ARU surveys more severely than in-person surveys (Digby et al 2013), and it is possible we did not experience the true effect wind has on recordings because our experimental design did not include wind gusts, which would tend to cause recordings to "clip" (Zakis 2011) and further affect detection. Additionally, white noise may not have been ideal to represent sound produced by wind in open habitats, where greater environmental noise can occur at lower frequencies (Zakis 2011), thereby masking only portions of a call and not affecting detection as severely (Koper et al 2015).…”

“…Past research suggests that wind affects detection of calls in ARU surveys more severely than in-person surveys (Digby et al 2013), and it is possible we did not experience the true effect wind has on recordings because our experimental design did not include wind gusts, which would tend to cause recordings to "clip" (Zakis 2011) and further affect detection. Additionally, white noise may not have been ideal to represent sound produced by wind in open habitats, where greater environmental noise can occur at lower frequencies (Zakis 2011), thereby masking only portions of a call and not affecting detection as severely (Koper et al 2015). However, our use of white noise was likely appropriate to simulate the interference caused by leaf rustle in deciduous forests and likely dense cattail vegetation, which tend to follow a similar sound profile (Turnbull, personal commuication).…”

Robust wind noise detection

“…A medium-sized, behind-the-ear hearing aid ("BTE2" from [4]), with a typical spacing of 13 mm between its unmatched microphones, was modified so a thin, shielded, multi-core cable entered near its base (well clear of the microphone ports) and was connected to each microphone's power, ground, and signal terminals. All other hearing-aid circuits were disconnected from the microphones and unpowered.…”

“…For instance, surveys report a 58 % satisfaction rate with hearing-aid performance in wind, compared with 61 % for noisy situations and 91 % for one-on-one conversation in quiet [3]. Hearing-aid wind noise levels can exceed lowfrequency speech levels at a wind speed of only 3 m/s (11 km/h) and also exceed high-frequency speech levels at 6 m/s (22 km/h) [4]. Speech masking by wind noise may occur at even higher frequencies in the impaired auditory system.…”

“…Speech masking by wind noise may occur at even higher frequencies in the impaired auditory system. Wind noise can also clip hearing-aid electret microphone circuits by 12 m/s (43 km/h), resulting in equivalent input levels of up to 116 dB SPL [4]. Therefore, aggressive windnoise reduction algorithms are needed for reducing the undesirable effects of wind noise on listening comfort and possibly speech understanding, and a reliable means of detecting the presence or absence of wind noise is important for appropriately controlling such algorithms.…”