Effects of the acoustical dynamic range on speech recognition with cochlear implants.

The amplitude compression function in a speech processor for cochlear implants maps the wide acoustical dynamic range of sounds into the smaller electrical dynamic range available on the implanted electrodes. In this study, we examined the effects of systematic variations of the acoustical dynamic range of the compression function on speech recognition with cochlear implants. Statistical measures of the amplitude distribution of speech sounds were made in each channel of a research speech processor providing more than 50 dB of input signal-to-noise ratio. Several systematic variations of the dynamic range of the compression function were implemented on this basis, and speech recognition was determined using vowel and consonant identification tests in three experienced cochlear implant users. Results demonstrated that the acoustical dynamic range of the compression function does have a significant effect on speech recognition with cochlear implants. They suggest that a dynamic range of about 45 dB is necessary for optimal speech recognition.