Improving effectiveness of directional microphones with Soft Level Directivity

Abstract

While today’s hearing instrumen ts have many features, and new features are introduced each year, one feature has withstood the test of time for the past 40 years – directional microphone technology. The application of d irectional technology is one of the few methods of impro ving speech u nderstanding in background noise, a patient benefit which has been supported in evidence-based r eviews (e.g. Bentler, 2005). Most modern directional hearing aids are automatic and adaptive. Automatic, in that based on the signal d etected by the classification system, the directional tec hnology will either be activated or de-activated (omni directional amplification) for individual listening situations. Adaptive, meaning that the directional polar pattern will automatically be altered to maximize speech understan ding for a given speech and noise condition, which now even includes switching to anti-cardioid when speech is from behind the hearing aid user (see Chalupper et al., 2011). When counseling patients regarding the benefits of directional technology, we often mention specific listening situations where benefit would be expected—parties, noisy restaurants, large groups, etc. In general, we talk about listening situations where the speech and noise are rel atively loud, ~70 dB SPL or greater. But there ar e many troublesome listening situations, also with an adverse si gnal-to-noise (SNR) ratio, where the speech and noise si gnals are not as intense, maybe only 60 dB SPL, 50 dB SPL, or even softer. While we have made many advances in d irectional technology ov er the years, this is an area where improvement is still needed, and is the focus of this paper.