디지털 보청기 성능 검사 및 피팅과 방향성에 관한 연구

Abstract

This paper describes two aspects of digital hearing aids specification test. One is fitting and the other is directivity. These two functional features of digital hearing aids specification test were studied in both theoretical and experimental methods. The most recent trend of digital hearing aids specification test is described in chapter 2, and the developed fitting technique of digital hearing aids is explained in chapter 3, and the directional hearing aids are researched in chapter 4. In chapter 3, DSP chip parameters of a digital hearing aid (HA) are to be optimally selected or fitted for hearing impaired persons. The more precise parameter fitting guarantees the better compensation of the hearing loss (HL). Digital HAs adopt DSP chips for more precise fitting of various HL threshold curve patterns. A specific DSP chip such as Gennum GB3211 was designed and manufactured in order to match up to about 4.7 billion different possible HL cases with combination of 7 limited parameters. This chapter deals with a digital HA fitting program which is developed for optimal fitting of GB3211 DSP chip parameters. The fitting program has completed features from audiogram input to DSP chip interface. The compensation effects of the microphone and the receiver are also included. The paper shows some application examples. In chapter 4, two twin microphones are used to produce particular patterns of binaural directivity by time delays between the twin microphones. The boundary element method (BEM) is used for the simulation of the sound pressure field around the KEMAR head model in order to quantify the acoustic head effect. The sound pressure onto the microphone is calculated by the BEM to an incident sound pressure. Then a planar directivity pattern is formed by four sound pressure signals from four microphones. The optimal binaural directivity pattern can be achieved by adjusting time delays at each frequency while maintaining the forward beam pattern is relatively bigger than the backward beam pattern. The simulation results are verified by the experimental measurement.