Effects of a nonlinear digital hearing aid amplifying in the time domain

The effects of a nonlinear, digital hearing aid on the perception of sentences in a quiet environment were examined for 12 patients with profound sensorineural hearing impairments. This hearing aid was equipped with a compression circuit, which divides the waveform in the time domain by zero-cross points, and then amplifies each waveform to an fixed amplitude. To reduce the susceptibility to background noise, input signals less than a certain level were amplified linearly, and this level was easily adjustable. Three out of 12 (25.0%) patients understood more than 50% of the phrases in typical Japanese sentences at all of the pre-set sound level (50, 60, 70 and 80 dBSPL). Furthermore, this device offered better perception than linear amplification (Rion HA70 or 73) in 8 out of 12 (66.7%) subjects, and was superior to the subjects' own linear hearing aids in 5 out of 10 (50.0%) cases. These results indicate that this hearing aid is beneficial for some subjects.