Expansion as a Tool for Adaptation to Amplification

ABSTRACT

Wide dynamic range compression (WDRC) has been successful at managing recruitment and reducing the discomfort of loud stimuli while making soft speech audible. However, WDRC can contribute to the complaint that hearing aids are noisy and that soft environmental sounds are abnormally loud. This situation can result in annoyance, stress, listener fatigue, and the possibility of a compromised signal-to-noise ratio for soft speech. Audio expansion is a tool that can be used to minimize these complaints. Although audio expansion has been in wide use as a noise reduction tool in telecommunications and professional audio for several decades, its use in hearing aids is comparatively recent. To understand better how expansion can be used to promote listener comfort and adaptation to hearing aid use, this article will present a basic review of expansion parameters. Subsequent sections will examine how expansion has been applied in hearing aids and how it behaves from a clinical standpoint. Finally, the use of expansion in multichannel WDRC hearing aid fittings will be discussed with a view toward improving listening comfort and helping new hearing aid users adapt to amplification.

KEYWORD

Expansion - noise reduction - listening comfort - adaptation - amplification

REFERENCES

• 1 Villchur E. Signal processing to improve speech intelligibility in perceptive deafness.  J Acoust Soc Am . 1973;  53 1646-1657
• 2 Yanick P, Drucker H. Signal processing to improve intelligibility in the presence of noise for persons with ski-slope hearing impairment.  IEEE Trans Acoust Speech Signal Process . 1976;  24 507-512
• 3 Walker G, Byrne D, Dillon H. The effects of multichannel compression/expansion amplification on the intelligibility of nonsense syllables in noise.  J Acoust Soc Am . 1984;  76 746-757
• 4 Nicolet Instrument Corporation. U.S. Patent 4,887,299, 1989
• 5 Kates J. U.S Patent 4,454,609, 1984
• 6 Preves D, Fortune T, Woodruff B, Newton J. Strategies for enhancing the consonant to vowel intensity ratio with in the ear hearing aids.  Ear Hear . 1991;  139S-153S (139S-153S)
• 7 Sammeth C, Tetzeli M, Ochs M. Consonant recognition performance of hearing-impaired listeners using one linear and three nonlinear hearing aids.  J Am Acad Audiol . 1996;  7 240-250
• 8 Bray V, Chabries D, Davis K, Johnson J. Digital signal processing (DSP) derived from a nonlinear auditory model. AAA, Los Angeles, Poster Session, 1998
• 9 Ghent R, Nilsson M, Bray V. Uses of expansion to promote listening comfort with hearing aids. AAA, Chicago, Poster Session, 2000
• 10 Skinner M. Hearing Aid Evaluation.  Englewood Cliffs, NJ: Prentice Hall; 1988
• 11 Nilsson M, Soli S, Sullivan J. Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise.  J Acoust Soc Am . 1994;  95 1085-1099
• 12 American National Standards Institute. Specification of Hearing Aid Characteristics ANSI S3.22-1996. New York: ANSI; 1996
• 13 American National Standards Institute. Methods of Measurement of Real-Ear Performance Characteristics of Hearing Aids ANSI S3.46-1997. New York: ANSI; 1997
• 14 American National Standards Institute. Maximum Permissible Ambient Noise Levels for Audiometric Test Rooms ANSI S3.1-1991. New York: ANSI; 1991
• 15 Ghent R, Nilsson M, Bray V, Johnson J. Expansion as a sound processing tool in hearing aids. AAA, Miami Beach, Poster Session, 1999
• 16 Mueller H G, Palmer C. Verification and validation of normal loudness perception. Instructional Course, AAA 11th Annual Convention, Miami Beach, FL, 1999
• 17 Kuk F, Lau C. Effect of hearing aid experience on preferred insertion gain selection.  J Am Acad Audiol . 1996;  7 274-281