We designed a new type of nonlinear digital hearing aid (TD-1) with near-instantaneous amplitude compression for sensorineural hearing-impaired people. The amplification method utilized by the TD-1 normalizes the signal waveforms within a time window bounded by two adjacent positive going zero-crossing points. The signals within this window are amplified so that the maximum amplitude reaches a preset value, thus allowing a consistent peak amplitude to be maintained. To test this, we examined the efficacy of the TD-1 device in 31 patients with sensorineural hearing loss. When tested for recognition of Japanese sentences in a quiet environment, 7 of 25 (28.0%) subjects wearing the TD-1 showed a 20% or greater increase in the maximum intelligibility score than that obtained when wearing their own linear hearing aids. In addition, 7 of 31 (22.6%) subjects showed the same increase with the TD-1 relative to that obtained when they wore HA70 or HA73 devices (Rion Co., Ltd., Tokyo, Japan), which are conventional analogue hearing aids. These results indicate that TD-1 can be effective for patients with sensorineural hearing loss.
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