Speech Perception in Noise with a Harmonic Complex Excited Vocoder

  • Tyler H. Churchill
  • Alan Kan
  • Matthew J. Goupell
  • Antje Ihlefeld
  • Ruth Y. Litovsky
Research Article


A cochlear implant (CI) presents band-pass-filtered acoustic envelope information by modulating current pulse train levels. Similarly, a vocoder presents envelope information by modulating an acoustic carrier. By studying how normal hearing (NH) listeners are able to understand degraded speech signals with a vocoder, the parameters that best simulate electric hearing and factors that might contribute to the NH-CI performance difference may be better understood. A vocoder with harmonic complex carriers (fundamental frequency, f0 = 100 Hz) was used to study the effect of carrier phase dispersion on speech envelopes and intelligibility. The starting phases of the harmonic components were randomly dispersed to varying degrees prior to carrier filtering and modulation. NH listeners were tested on recognition of a closed set of vocoded words in background noise. Two sets of synthesis filters simulated different amounts of current spread in CIs. Results showed that the speech vocoded with carriers whose starting phases were maximally dispersed was the most intelligible. Superior speech understanding may have been a result of the flattening of the dispersed-phase carrier’s intrinsic temporal envelopes produced by the large number of interacting components in the high-frequency channels. Cross-correlogram analyses of auditory nerve model simulations confirmed that randomly dispersing the carrier’s component starting phases resulted in better neural envelope representation. However, neural metrics extracted from these analyses were not found to accurately predict speech recognition scores for all vocoded speech conditions. It is possible that central speech understanding mechanisms are insensitive to the envelope-fine structure dichotomy exploited by vocoders.


cochlear implant simulation phase 


  1. Bingabr M, Espinoza-Varas B, Loizou PC (2008) Simulating the effect of spread of excitation in cochlear implants. Hear Res 241:73–79PubMedCentralPubMedCrossRefGoogle Scholar
  2. Carlyon RP (1996) Spread of excitation produced by maskers with damped and ramped envelopes. J Acoust Soc Am 99:3647–3655CrossRefGoogle Scholar
  3. Chen F, Loizou PC (2011) Predicting the intelligibility of vocoded speech. Ear Hear 32:331–338PubMedCentralPubMedCrossRefGoogle Scholar
  4. Deeks JM, Carlyon RP (2004) Simulations of cochlear implant hearing using filtered harmonic complexes: implications for concurrent sound segregation. J Acoust Soc Am 115:1736–1746PubMedCrossRefGoogle Scholar
  5. Dorman MF, Loizou PC, Rainey D (1997) Speech intelligibility as a function of the number of channels of stimulation for signal processors using sine-wave and noise-band outputs. J Acoust Soc Am 102:2403–2411PubMedCrossRefGoogle Scholar
  6. Dudley H (1939) Remaking speech. J Acoust Soc Am 11:169–177CrossRefGoogle Scholar
  7. Eskridge EN, Galvin JJ, Aronoff JM, Li T, Fu QJ (2012) Speech perception with music maskers by cochlear implant users and normal hearing listeners. J Speech Lang Hear Res 55:800–810PubMedCrossRefGoogle Scholar
  8. Friesen LM, Shannon RV, Baskent D, Wang X (2001) Speech recognition in noise as a function of the number of spectral channels: comparison of acoustic hearing and cochlear implants. J Acoust Soc Am 110:1150–1163PubMedCrossRefGoogle Scholar
  9. Fu QJ, Nogaki G (2005) Noise susceptibility of cochlear implant users: the role of spectral resolution and smearing. J Assoc Res Otolaryngol 6:19–27PubMedCentralPubMedCrossRefGoogle Scholar
  10. Fu QJ, Shannon RV, Wang X (1998) Effects of noise and spectral resolution on vowel and consonant recognition: acoustic and electric hearing. J Acoust Soc Am 104:3586–3596PubMedCrossRefGoogle Scholar
  11. Fu QJ, Chinchilla S, Galvin JJ (2004) The role of spectral and temporal cues in voice gender discrimination by normal-hearing listeners and cochlear implant users. J Assoc Res Otolaryngol 5:253–260PubMedCentralPubMedCrossRefGoogle Scholar
  12. Greenwood DD (1990) A cochlear frequency-position function for several species—29 years later. J Acoust Soc Am 87:2592–2605PubMedCrossRefGoogle Scholar
  13. Heinz MG, Swaminathan J (2009) Quantifying envelope and fine-structure coding in auditory nerve responses to chimaeric speech. J Assoc Res Otolaryngol 10:407–423PubMedCentralPubMedCrossRefGoogle Scholar
  14. Hervais-Adelman AG, Davis MH, Johnsrude IS, Taylor KJ, Carlyon RP (2011) Generalization of perceptual learning of vocoded speech. J Exp Psychol Hum Percept Perform 37:283–295PubMedCrossRefGoogle Scholar
  15. Joris PX (2003) Interaural time sensitivity dominated by cochlea-induced envelope patterns. J Neurosci 23:6345–6350PubMedGoogle Scholar
  16. Kates JM (2011) Spectro-temporal envelope changes caused by temporal fine structure modification. J Acoust Soc Am 129:3981–3990PubMedCrossRefGoogle Scholar
  17. Kiang NY, Moxon EC (1972) Physiological considerations in artificial stimulation of the inner ear. Ann Otol 81:714–730Google Scholar
  18. Kohlrausch A, Sander A (1995) Phase effects in masking related to dispersion in the inner ear. J Acoust Soc Am 97:1817–1829PubMedCrossRefGoogle Scholar
  19. Loizou PC (2006) Speech processing in vocoder-centric cochlear implants. In: A. Moller (ed) Cochlear and brainstem implants, vol 64. Karger, Basel, pp 109–143Google Scholar
  20. Louage DH, van der Heijden M, Joris PX (2004) Temporal properties of responses to broadband noise in the auditory nerve. J Neurophysiol 91:2051–2065PubMedCrossRefGoogle Scholar
  21. Lu T, Carroll J, Zeng FG (2007) On acoustic simulations of cochlear implants. Conference on Implantable Auditory Prostheses, Lake Tahoe, CAGoogle Scholar
  22. Moxon EC (1971) Neural and mechanical responses to electrical stimulation of the cat’s inner ear. Dissertation, Massachusetts Institute of TechnologyGoogle Scholar
  23. Nelson PB, Jin S-H, Carney AE, Nelson DA (2003) Understanding speech in modulated interference: cochlear implant users and normal-hearing listeners. J Acoust Soc Am 113:961–968PubMedCrossRefGoogle Scholar
  24. Schroeder MR (1966) Vocoders: analysis and synthesis. Proc IEEE 54:720–734CrossRefGoogle Scholar
  25. Schroeder MR (1970) Synthesis of low peak-factor signals and binary sequences with low autocorrelation. IEEE Trans Inf Theory 16:85–89Google Scholar
  26. Shamma S, Lorenzi C (2013) On the balance of envelope and temporal fine structure in the encoding of speech in the early auditory system. J Acoust Soc Am 133:2818–2833PubMedCrossRefGoogle Scholar
  27. Shannon RV, Zeng F-G, Kamath V, Wygonski J, Ekelid M (1995) Speech recognition with primarily temporal cues. Science 270:303–304PubMedCrossRefGoogle Scholar
  28. Souza P, Rosen S (2009) Effects of envelope bandwidth on the intelligibility of sine- and noise-vocoded speech. J Acoust Soc Am 126:792–805PubMedCentralPubMedCrossRefGoogle Scholar
  29. Stone MA, Füllgrabe C, Moore BCJ (2008) Benefit of high-rate envelope cues in vocoder processing: effect of number of channels and spectral region. J Acoust Soc Am 124:2272–2282PubMedCrossRefGoogle Scholar
  30. Studebaker GA (1985) A “rationalized” arcsine transform. J Speech Hear Res 28:455–462PubMedGoogle Scholar
  31. Swaminathan J, Heinz MG (2011) Predicted effects of sensorineural hearing loss on across-fiber envelope coding in the auditory nerve. J Acoust Soc Am 129:4001–4013PubMedCentralPubMedCrossRefGoogle Scholar
  32. Swaminathan J, Heinz MG (2012) Psychophysiological analyses demonstrate the importance of neural envelope coding for speech perception in noise. J Neurosci 32:1747–1756PubMedCentralPubMedCrossRefGoogle Scholar
  33. Van Deun L, Van Wieringen A, Wouters J (2010) Spatial hearing perception benefits in young children with normal hearing and cochlear implants. Ear Hear 31:702–713PubMedGoogle Scholar
  34. van Hoesel RJM, Tyler RS (2003) Speech perception, localization, and lateralization with bilateral cochlear implants. J Acoust Soc Am 113:1617–1630PubMedCrossRefGoogle Scholar
  35. Whitmal NA, Poissant SF, Freyman RL, Helfer KS (2007) Speech intelligibility in cochlear implant simulations: effects of carrier type, interfering noise, and subject experience. J Acoust Soc Am 122:2376–2388PubMedCrossRefGoogle Scholar
  36. Young E, Sachs M (1979) Representation of steady-state vowels in the temporal aspects of the discharge patterns of populations of auditory-nerve fibers. J Acoust Soc Am 66:1381–1403PubMedCrossRefGoogle Scholar
  37. Zilany MS, Bruce IC (2006) Modeling auditory-nerve responses for high sound pressure levels in the normal and impaired auditory periphery. J Acoust Soc Am 120:1446–1466Google Scholar
  38. Zilany MS, Bruce IC (2007) Representation of the vowel /ε/ in normal and impaired auditory nerve fibers: model predictions of responses in cats. J Acoust Soc Am 122:402–417PubMedCrossRefGoogle Scholar
  39. Zilany MS, Bruce IC, Nelson PC, Carney LH (2009) A phenomenological model of the synapse between the inner hair cell and auditory nerve: long-term adaptation with power-law dynamics. J Acoust Soc Am 126:2390–2412PubMedCentralPubMedCrossRefGoogle Scholar

Copyright information

© Association for Research in Otolaryngology 2014

Authors and Affiliations

  • Tyler H. Churchill
    • 1
  • Alan Kan
    • 1
  • Matthew J. Goupell
    • 2
  • Antje Ihlefeld
    • 3
  • Ruth Y. Litovsky
    • 1
  1. 1.Waisman CenterUniversity of Wisconsin—MadisonMadisonUSA
  2. 2.Department of Hearing and Speech SciencesUniversity of Maryland—College ParkCollege ParkUSA
  3. 3.Center for Neural ScienceNew York UniversityNew YorkUSA

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