Derivation of Frequency-Gain Characteristics for Maximizing Speech Reception in Noise Hearing aid gain-assignment schemes known as "prescriptions" were not designed for fitting hearing aids that modify their frequency responses to reduce background noise interference. Rather, prescriptions were developed for hearing aids having single, fixed frequency responses and aim to optimize speech reception in relatively quiet environments. Even though prescriptions do ... Research Article
Research Article  |   August 01, 1995
Derivation of Frequency-Gain Characteristics for Maximizing Speech Reception in Noise
 
Author Affiliations & Notes
  • Christine M. Rankovic
    Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge
  • Currently affiliated with Northeastern University
    Currently affiliated with Northeastern University×
  • Contact author: Christine M. Rankovic, PhD, Northeastern University, Department of Speech-Language Pathology and Audiology, 360 Huntington Avenue, 133 Forsyth, Boston, MA 02115.
    Contact author: Christine M. Rankovic, PhD, Northeastern University, Department of Speech-Language Pathology and Audiology, 360 Huntington Avenue, 133 Forsyth, Boston, MA 02115.×
Article Information
Hearing & Speech Perception / Acoustics / Hearing Disorders / Hearing Aids, Cochlear Implants & Assistive Technology / Hearing / Research Articles
Research Article   |   August 01, 1995
Derivation of Frequency-Gain Characteristics for Maximizing Speech Reception in Noise
Journal of Speech, Language, and Hearing Research, August 1995, Vol. 38, 913-929. doi:10.1044/jshr.3804.913
History: Received February 14, 1994 , Accepted February 17, 1995
 
Journal of Speech, Language, and Hearing Research, August 1995, Vol. 38, 913-929. doi:10.1044/jshr.3804.913
History: Received February 14, 1994; Accepted February 17, 1995

Hearing aid gain-assignment schemes known as "prescriptions" were not designed for fitting hearing aids that modify their frequency responses to reduce background noise interference. Rather, prescriptions were developed for hearing aids having single, fixed frequency responses and aim to optimize speech reception in relatively quiet environments. Even though prescriptions do not apply to noisy conditions specifically, they embody the trade between maximizing speech audibility and maintaining loudness comfort that is critical to frequency-gain characteristic selection independent of whether noise is present or absent. The articulation index (Al) was used to examine the extent to which prescriptions' deference to loudness comfort causes them to fall short of maximizing speech spectrum audibility, thereby revealing (roughly) the magnitude of the loudness control built into prescriptions. Als for speech amplified by an Al-maximizing rule (MAX Al) (Rankovic, Freyman, & Zurek, 1992) and according to several prescriptions were calculated as a function of hearing loss degree and configuration for quiet and noisy conditions. In quiet, Als for prescriptions were similar to one another when presented with the same audiogram but were drastically smaller than MAX Als, implying that prescriptions limit speech audibility to a large extent to prevent loudness discomfort. In noise, maximizing the Al required frequency-gain characteristics that were substantially different from prescription-assigned characteristics and that were unique to each noise/audiogram combination. A loudness constraint for the MAX Al scheme was developed to account for the gain discrepancy between prescription Als and MAX Als observed in the quiet condition, based on the highest comfortable loudness (HCL) equations presented by Cox (1989) in combination with a loudness model (von Paulus & Zwicker, 1972). The MAX Al scheme with the new loudness control was extended to specify frequency-gain characteristics expected to be optimal for several conditions containing noise, and examples are presented.

Acknowledgments
The author thanks P.M. Zurek for important contributions. Portions of this work were supported by Grants T32 DC00010, R01 DC00117, and R29 DC02127 from the National Institute of Deafness and Other Communicative Disorders and were presented at the annual meeting of the American Speech-Language-Hearing Association, November 1991, in Atlanta.
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