Speech dynamic range and its effect on cochlear implant performance

Top Cited Papers
Publisher Website
Google Scholar
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.