The long term objective of the proposed program is the development, design and manufacture of a signal processor-controlled hearing aid to maintain the overall sound pressure level (SPL) and the spectrum at the eardrum within optimum limits for the hearing impaired individual for allexpected input spectra and input levels. An additional feature will be an increase in signal-to-noise ratio of the aided signal. The signal processing will be based on the actual eardrum SPL, determined from an acoustic feedback signal obtained by a microphone or probe in the ear canal. For all expected input levels, the spectrum of the eardrum sound pressure is controlled by the processor, so that the peak SPL in any 1/3-octave interval does not exceed the individual's loudness discomfort level (LDL) while still maintaining the desired spectrum and SPL at its most effective value. The processor compares the inputs and outputs for each filter and the gain in each channel is then adjusted (on a real time basis) to obtain the desired output for the band. Determination of averaging times for both the input and output signals are significant and will constitute a major element in the study. Phase I objective is to breadboard this system (without) the signal-to-noise ratio improvement) and test it on a manikin, equipped with a ANSI S3.25-1979 simulator.
