8-channel digital filter bank for hearing aid use: preliminary results in monaural, diotic and dichotic modes.

A digital 8-channel signal processing system has been implemented using a TMS 320C25 signal processor. Tests with hearing-impaired subjects showed that the system allows a better fit to a specified frequency response than when using conventional aids with analog filtering. The filter bank has also been tested in dichotic listening experiments, where odd-number channels were fed to one ear and even-number channels to the other. The preliminary results on three hearing-impaired subjects in repeated tests of speech recognition in noise showed an improvement in the order of 2 dB in speech-to-noise ratio for 50% correct recognition as compared to the complete broadband signal presented diotically. Temporal splitting of the signal by periodically switching of the odd and even bands between left and right ears did not show any improvement.