Development of a prototype portable binaural digital hearing aid

Summary form only given. For a hearing aid user to perform binaural directional hearing in noisy environments, it is important to maintain at audible levels the binaural cues (interaural time and level differences) that would be present if the hearing aid were not in place. We have developed a wearable prototype digital hearing aid and personal computer (PC) based methods of digital filter design for evaluation of the effectiveness of this method. The body-worn prototype processor utilizes a Motorola 56000-series DSP chip to implement the filtering and amplification for both ears via cabled ITE ear modules. Up to four different user-selectable algorithms can be programmed in the processor. Binaural fitting of the processor is accomplished in two steps: hearing aid equalization (HAE) and hearing loss compensation (HLC). The HAE is achieved with an FIR filter which equalizes the amplitude and phase insertion effects of the ear modules and maintains the binaural cues with the modules in place. The HLC for each ear is also achieved with an FIR filter and associated gain. The HAE and HLC filters are convolved to produce a single filter. A detailed description is given of the processor, fitting algorithms, methods and accuracy of fittings, as determined from in situ probe tube measurements, and the hardware and software comprising the binaural hearing aid. Results from field trials with the portable processors are also reported