Measurement and Intelligibility Optimization of Directional Microphones for Use in Hearing Aid Devices
A person with normal hearing has the ability to understand speech in noise when tested at signal-to-noise ratios as low as -5 dB. In order for hearing-impaired individuals to achieve similar comprehension, it is necessary to improve the signal-to-noise ratio of such speech signals by 5 to 15 dB. No electronic signal processing technique has been shown to provide such improvements as those obtainable with directional microphones. This paper will focus on the development and use of measurement techniques for evaluating and optimizing directional microphones designed for use in Behind-The-Ear (BTE) and In-The-Ear (ITE) hearing aids. Data on directional performance will be presented for current omni-directional and directional hearing aid designs, optimized for BTE applications, as well as a new directional microphone design suitable for use in ITE hearing aids. The concept of an Articulation Index weighted Directivity Index (AI-DI) will be developed and presented as a meaningful measure of intelligibility performance for microphones.
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