An Integrative Evaluation of the Efficacy of a Directional Microphone and Noise Reduction Algorithm Under Realistic Signal-to-Noise Ratios

Abstract

Background: Many studies on the efficacy of directional microphones (DIRMs) and noise reduction (NR)algorithms were not conducted under realistic signal-to-noise ratio (SNR) conditions. A Repeat–RecallTest (RRT) was developed previously to partially address this issue.<br />Purpose: This study evaluated whether the RRT could provide a more comprehensive understanding ofthe efficacy of a DIRM and NR algorithm under realistic SNRs. Possible interaction with listener workingmemory capacity (WMC) was assessed.<br />Research Design: This study uses a double-blind, within-subject repeated measures design.<br />Study Sample: Nineteen listeners with a moderate degree of hearing loss participated.<br />Data Collection and Analysis: The RRT was administered with participants wearing the study hearingaids (HAs) under two microphones (omnidirectional versus directional) by two NR (on versus off) conditions.Speech was presented from 0° at 75 dB SPL and a continuous noise from 180° at SNRs of 0, 5,10, and 15 dB. The order of SNR and HA conditions was counterbalanced across listeners. Each testcondition was completed twice in two 2-hour sessions separated by one month.<br />Results: The recall scores of listeners were used to group listeners into good and poor WMC groups.Analysis using linear mixed-effects models revealed significant effects of context, SNR, and microphonefor all four measures (repeat, recall, listening effort, and tolerable time). NR was only significant on thelistening effort scale in the DIRM mode at an SNR of 5 dB. Listeners with good WMC performed better onall measures of the RRT and benefitted more from context. Although DIRM benefitted listeners with goodand poor WMC, the benefits differed by context and SNR.<br />Conclusions: The RRT confirmed the efficacy of DIRM and NR on several outcome measures underrealistic SNRs. It also highlighted interactions between WMC and sentence context on feature efficacy.<br />