Comparing Binaural Pre-processing Strategies II

Abstract

Several binaural audio signal enhancement algorithms were evaluated with respect to their potential to improve speech intelligibility in noise for users of bilateral cochlear implants (CIs). 50% speech reception thresholds (SRT50) were assessed using an adaptive procedure in three distinct, realistic noise scenarios. All scenarios were highly nonstationary, complex, and included a significant amount of reverberation. Other aspects, such as the perfectly frontal target position, were idealized laboratory settings, allowing the algorithms to perform better than in corresponding real-world conditions. Eight bilaterally implanted CI users, wearing devices from three manufacturers, participated in the study. In all noise conditions, a substantial improvement in SRT50 compared to the unprocessed signal was observed for most of the algorithms tested, with the largest improvements generally provided by binaural minimum variance distortionless response (MVDR) beamforming algorithms. The largest overall improvement in speech intelligibility was achieved by an adaptive binaural MVDR in a spatially separated, single competing talker noise scenario. A no-pre-processing condition and adaptive differential microphones without a binaural link served as the two baseline conditions. SRT50 improvements provided by the binaural MVDR beamformers surpassed the performance of the adaptive differential microphones in most cases. Speech intelligibility improvements predicted by instrumental measures were shown to account for some but not all aspects of the perceptually obtained SRT50 improvements measured in bilaterally implanted CI users.

Improving Speech Recognition in Bilateral Cochlear Implant Users by Listening With the Better Ear

“…For many listeners, different SRTs were achieved depending on which ear was attended to, suggesting a better ear for attending to speech in the presence of a masker. The phenomenon of a better ear has also been reported in a number of other studies (e.g., Baumgärtel, Hu, et al., 2015 ; Litovsky et al., 2006 ; van Hoesel & Tyler, 2003 ). There are a number of reasons why CI users have a better or preferred ear for listening.…”

“…Depending on the time and frequencies where this occurs, the perceptual consequences on intelligibility may be situation dependent. To provide an objective measure for this algorithm, the intelligibility-weighted SNR (iSNR) ( Greenberg, Peterson, & Zurek, 1993 ) was estimated using the method described in Baumgärtel, Krawczyk-Becker, et al. (2015) .…”

“…Many of these approaches have either applied an ideal binary mask that fully eliminate time-frequency bins that have poor SNR (e.g., Hu & Loizou, 2008 ; Koning, Madhu, & Wouters, 2015 ), or more sophisticated filtering algorithms that reduce the noise by estimating the noise power (e.g., Goldsworthy, Delhorne, Desloge, & Braida, 2014 ; Hersbach, Grayden, Fallon, & McDermott, 2013 ; Koning et al., 2015 ), or enhancing the target signal (e.g., Healy, Delfarah, Vasko, Carter, & Wang, 2017 ; Kokkinakis, Azimi, Hu, & Friedland, 2012 ). Baumgärtel, Hu et al. (2015) provides a thorough evaluation of some of the most promising algorithms and showed that these algorithms can provide up to 7 dB improvement in CI users in demanding noisy conditions.…”

Cochlear implant research and development in the 21st century: A critical update

“…For conditions that fulfil this assumption (e.g. target speech in front and noise at one side of the listener), several studies have reported significant improvements in terms of correctly identified sentences (van Hoesel and Clark, 1995;Chung et al, 2006;Chung and Zeng, 2009) and speech reception threshold (SRT), defined as the SNR required for 50%-Carlyon & Goehring -21 st century CI 7 correct performance (Wouters and Vanden Berghe, 2001;Spriet et al, 2007;Hersbach et al, 2012;Baumgartel et al, 2015). Improvements ranged from 3.7 up to 16 dB in SRT, which can be considered as very substantial, and have been obtained using single-blinded (Chung et al, 2006;Chung and Zeng, 2009) or double-blinded designs (Spriet et al, 2007).…”

Binaural (pre)processing for contralateral sound field attenuation and improved speech-in-noise recognition

“…For users of bilateral devices, monaural SNR-enhancement algorithms are often applied separately in each device, an approach that can distort inter-aural time (ITD) and level differences (ILDs) and thus hinder the localization of sound sources (e.g., Cornelis et al, 2012; Doclo et al, 2015). The introduction of assistive listening devices that swap signals between the two ears has spawned the development of binaural pre-processing algorithms, i.e., systems that couple the functioning of two devices (Hamacher et al, 2005; Moore, 2007; Baumgärtel et al, 2015a, 2015b). One approach consists of detecting binaural cues and re-introducing them after the SNR is enhanced separately in each ear (see the review of Doclo et al, 2015).…”