Noise as a problem for the hearing impaired

This paper gives some results of current research on the elevation of the Speech-Reception Threshold (SRT) in noise due to hearing impairment. The experiments were carried out with simple sentences as speech material. The noise had the same spectrum as the long-term average of the speech signal. The SRT was the level at which 50% of the sentences were repeated correctly by the listener. Roughly, in the case of steady-state noise, a 3 dB higher speech-to-noise ratio is required. In the case of a fluctuating interfering sound (e.g., a competing peaker), the critical speech-to-noise ratio is about 8.5 dB higher than for normal-hearing listeners. Subsequent data suggest that for the hearing-impaired listeners the benefit of binaural hearing is about 3 dB less than in normal hearing. Since a difference of 1 dB in SRT corresponds with 16–20% difference in the intelligibility score of sentences, the data can explain why many hearing-impaired people have difficulties in understanding speech at speech-to-noise ratios acceptable for normal-hearing listeners.