Sigfrid D. Soli
House Ear Inst., 2100 W. 3rd St., Los Angeles, CA 90057
For a hearing aid wearer to perform binaural sound localization and to utilize directional hearing in noisy environments, it may be important to maintain at audible levels the binaural cues (i.e., interaural time and level differences) present without the hearing aid(s) in place. A method of achieving this hearing aid fitting goal for use with a prototype digital signal processing hearing aid has been developed. The method includes two major steps: hearing aid equalization (HAE) and hearing loss compensation (HLC). HAE is achieved with an FIR filter, which equalizes the amplitude and phase insertion effects of the hearing aids and maintains the binaural cues with the hearing aid(s) in place. The HAE filter coefficients are obtained from in situ probe tube measures of aided and unaided test signals using optimal filter calculations. HLC is also achieved with an FIR filter and associated gain. The HLC filter coefficients are obtained by using a weighted least-squares filter design technique. The target response for the HLC filter is determined from measures of electrical signal levels in the hearing aid circuit during threshold tests and during reference signal presentations in the sound field. The HAE and HLC filters are convolved to produce a single filter. A description of the fitting procedure will be provided, as well as examples of its use with hearing impaired individuals.