Speech dynamic range and its effect on cochlear implant performance

Abstract

This study examines optimal conversions of speech sounds to audible electric currents in cochlear-implant listeners. The speech dynamic range was measured for 20 consonants and 12 vowels spoken by five female and five male talkers. Even when the maximal root-mean-square (rms) level was normalized for all phoneme tokens, both broadband and narrow-band acoustic analyses showed an approximately 50-dB distribution of speech envelope levels. Phoneme recognition was also obtained in ten CLARION implant users as a function of the input dynamic range from 10 to 80 dB in 10-dB steps. Acoustic amplitudes within a specified input dynamic range were logarithmically mapped into the 10-20-dB range of electric stimulation typically found in cochlear-implant users. Consistent with acoustic data, the perceptual data showed that a 50-60-dB input dynamic range produced optimal speech recognition in these implant users. The present results indicate that speech dynamic range is much greater than the commonly assumed 30-dB range. A new amplitude mapping strategy, based on envelope distribution differences between consonants and vowels, is proposed to optimize acoustic-to-electric mapping of speech sounds. This new strategy will use a logarithmic map for low-frequency channels and a more compressive map for high-frequency channels, and may improve overall speech recognition for cochlear-implant users.

Use of Amplitude Modulation Cues Recovered from Frequency Modulation for Cochlear Implant Users When Original Speech Cues Are Severely Degraded

“…60 dB (Fig. 10B), which is consistent with a previous report (Zeng et al 2002). A change in the IDR does not change the acoustic peak amplitudes that are mapped to the subjects' most comfortable levels.…”

“…The dynamic range of typical speech sounds is between 30 and 60 dB (Zeng et al 2002). The speech processor must fit speech sounds into this narrow dynamic range for CI users.…”

Effects of Presentation Level on Phoneme and Sentence Recognition in Quiet by Cochlear Implant Listeners

“…These results led the authors to conclude that a 30-dB IDR provides adequate speech information for phoneme identification, even when spectral resolution is restricted to four spectral channels. More recently, Zeng et al (2002) measured the effects of IDR on vowel and consonant recognition in Clarion cochlear implant users with the CIS strategy, for IDR settings ranging from 10 to 60 dB. In contrast to the Fu and Shannon results, these authors found that IDRs of 50 to 60 dB yielded the highest scores for consonant recognition in quiet, and that IDRs of 40 to 50 dB yielded the highest scores for vowel recognition in quiet.…”

The Development of the Nucleus® Freedom™ Cochlear Implant System

“…This was consistent with the results from the previous study. 71 For sentences in noise, there was no significant difference in scores for the 3 IIDRs. However, subjective preferences showed that some subjects found the 56-dB IIDR uncomfortable in everyday listening environments.…”

“…Recent studies by Zeng et al 71 showed that the acoustic dynamic range was 46 dB for vowels and 47 dB for consonants. When vowel and consonant perception in CI recipients was tested in quiet, an IIDR of approximately 50 dB gave the optimum vowel and consonant scores.…”