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Journal of the Acoustical Society of America / Volume 124 / Issue 4 / PSYCHOLOGICAL ACOUSTICS [66]

Benefit of high-rate envelope cues in vocoder processing: Effect of number of channels and spectral region

J. Acoust. Soc. Am. Volume 124, Issue 4, pp. 2272-2282 (2008); (11 pages)

Michael A. Stone, Christian Füllgrabe, and Brian C. J. Moore

Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, United Kingdom

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In cochlear implants, or vocoder simulations of cochlear implants, the transmission of envelope cues at high rates (related to voice fundamental frequency, f0) may be limited by the widths of the filters used to form the channels and/or by the cutoff frequency, flp, of the low-pass filters used for envelope extraction. The effect of varying flp in tone and noise vocoders was investigated for channel numbers, N, from 6 to 18. As N increased, the widths of the channels decreased. The value of flp was 45 Hz (envelope or “E” filter), or 180 Hz (pitch or “P” filter). The following combinations of cutoff frequencies were used for channels below and above 1500 Hz, respectively: EE, PE, EP, and PP. Results from a competing-talker task showed that the tone vocoder led to better intelligibility than the noise vocoder. The PP condition led to the best intelligibility and the EE condition to the worst. For N = 6, intelligibility was better for condition PE than for condition EP. For N = 18, the reverse was true. The results indicate that the channel bandwidths can compromise the transmission of f0-related envelope information, and suggest that vocoder simulations of cochlear-implant processing have limitations.

© 2008 Acoustical Society of America

ACKNOWLEDGMENTS

M.A.S. and B.C.J.M. were supported by the MRC (UK). C.F. was supported by a Marie-Curie fellowship from the EU. The authors thank Associate Editor Ken Grant and two reviewers for helpful comments on an earlier version of this paper.

Article Outline

  1. INTRODUCTION
  2. EXPERIMENT 1: EFFECTS OF N AND flp FOR NOISE AND TONE VOCODERS
    1. Vocoder design and processing condition
    2. Speech material
    3. Subjects, training, and experimental design
    4. Signal presentation
    5. Results
  3. EXPERIMENT 2: AVOIDING FLOOR AND CEILING EFFECTS
    1. Rationale
    2. Subjects and method
    3. Results
    4. Combined analysis of results for experiments 1 and 2
  4. DISCUSSION
    1. Influence of N on the benefit from high-rate envelope modulation information
    2. High-rate envelope modulation information improves both f 0 -related information and representation of envelope onset
    3. Comparison of noise and tone vocoders
    4. Implications for simulations of CI processing
  5. CONCLUSIONS

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KEYWORDS and PACS

Keywords

acoustic noise, acoustic signal processing, hearing aids, prosthetics, vocoders

PACS

  • 43.66.Ts

    Auditory prostheses, hearing aids

  • 43.66.Mk

    Temporal and sequential aspects of hearing; auditory grouping in relation to music

  • 43.71.Gv

    Measures of speech perception (intelligibility and quality)

ARTICLE DATA

History
Received 30 Aug 2007
Accepted 18 Jul 2008
Revised 10 Jul 2008
Digital Object Identifier
http://dx.doi.org/10.1121/1.2968678

PUBLICATION DATA

ISSN

0001-4966 (print)  

Publisher

$abstract.society.value is a Member of CrossRef Acoustical Society of America

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