Limitations of theoretical benefit from an adaptive directional system in reverberant environments

Hearing aids with adaptive and fixed two-microphone processing are currently available. Although the noise reduction increase of adaptive over fixed aids can theoretically be tens of dB, it is unclear if this benefit can be found with realistic processing and conditions. Thus, a theoretical analysis of the ability of today’s aids to attenuate jammers in “everyday” conditions [direct-reverberant ratio ⩽5.0 dB] is provided. Processing limitations restrict aids to wideband null steering through intermicrophone delay variation. Delay variation is predicted to provide maximally 2.0 dB more noise reduction than the best fixed system on average, and only at the highest direct-reverberant ratios.