Speech dynamic range and its effect on cochlear implant performance

Fan Gang Zeng, Ginger Grant, John Niparko, John Galvin, Robert Shannon, Jane Opie, Phil Segel

Research output: Contribution to journalArticlepeer-review

115 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)377-386
Number of pages10
JournalJournal of the Acoustical Society of America
Volume111
Issue number1 I
DOIs
StatePublished - 2002

ASJC Scopus subject areas

  • Acoustics and Ultrasonics

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