Evaluation of Noise Reduction in (digital) Hearing Aids

Researcher(s): L. Körössy, E.E., A.E. Hoetink, PhD.
Supervisor(s): prof. W.A. Dreschler, PhD.

Background:
Noise reduction may be one of the most important developments to improve the functionality of hearing aids in critical situations. Therefore, most (high end) hearing aids are equipped with a noise reduction system in one form or another. Different hearing aid manufacturers, however, implement noise reduction systems based on different noise reduction strategies. Information about noise reduction strategies that are implemented is seldomly provided and as a consequence the effect of different noise reduction systems on hearing aid output is largely unknown.
To study the effect of different noise reduction systems that are implemented in hearing aids, our laboratory has developed a new measurement system for the technical evaluation of noise reduction systems.

Aim:
Classification and optimization of noise reduction strategies for digital hearing aids.

Method:
The measurement system uses both non-modulated and (amplitude) modulated ICRA-noises, which are mixed in different Signal-to-Noise ratios. The (amplitude) modulated ICRA-noise is considered to represent a speech signal, whereas the non-modulated ICRA-noise represents background noise. By using these mixtures of ICRA-noises as the input of hearing aids and measuring the outputs, the effect of the noise reduction systems implemented in those hearing aids can be investigated as a function of Signal-to-Noise ratio.

Results:
Preliminary measurements on three hearing aids (reported in a paper published in Audiology 2001; 40:148-157) were used to fine tune the measurement system. With this measurement system, different noise reduction systems that are applied in a number of hearing aids have been tested and are being documented and classified.

Future research:
The data that is currently available will be supplemented by data from measurements on noise reduction systems that have recently become available. The results will be published in a paper that compares different noise reduction strategies and establishes the most important parameters of noise reduction systems. Additionally, in a follow-up study the perceptual effects will be investigated. By systematically varying the most important parameters, we will investigate the optimal settings of noise reduction algorithms.


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General Otology Prevention of hearing loss Auditory profile Rehabilitation Evaluation of Noise Reduction in (digital) Hearing Aids AZOS-project: Modified care model for hearing impaired listeners Classification of hearing aids in CLiQ Interactive fitting of hearing aids “Self learning” or trainable hearing aid Evaluation of advanced hearing aid features Optimalisation of hearing aids through paired comparisons Field trials with innovative hearing instruments The added value of a bilateral hearing aid fitting Hearing at work Publications Presentations	Evaluation of Noise Reduction in (digital) Hearing Aids Researcher(s): L. Körössy, E.E., A.E. Hoetink, PhD. Supervisor(s): prof. W.A. Dreschler, PhD. Background: Noise reduction may be one of the most important developments to improve the functionality of hearing aids in critical situations. Therefore, most (high end) hearing aids are equipped with a noise reduction system in one form or another. Different hearing aid manufacturers, however, implement noise reduction systems based on different noise reduction strategies. Information about noise reduction strategies that are implemented is seldomly provided and as a consequence the effect of different noise reduction systems on hearing aid output is largely unknown. To study the effect of different noise reduction systems that are implemented in hearing aids, our laboratory has developed a new measurement system for the technical evaluation of noise reduction systems. Aim: Classification and optimization of noise reduction strategies for digital hearing aids. Method: The measurement system uses both non-modulated and (amplitude) modulated ICRA-noises, which are mixed in different Signal-to-Noise ratios. The (amplitude) modulated ICRA-noise is considered to represent a speech signal, whereas the non-modulated ICRA-noise represents background noise. By using these mixtures of ICRA-noises as the input of hearing aids and measuring the outputs, the effect of the noise reduction systems implemented in those hearing aids can be investigated as a function of Signal-to-Noise ratio. Results: Preliminary measurements on three hearing aids (reported in a paper published in Audiology 2001; 40:148-157) were used to fine tune the measurement system. With this measurement system, different noise reduction systems that are applied in a number of hearing aids have been tested and are being documented and classified. Future research: The data that is currently available will be supplemented by data from measurements on noise reduction systems that have recently become available. The results will be published in a paper that compares different noise reduction strategies and establishes the most important parameters of noise reduction systems. Additionally, in a follow-up study the perceptual effects will be investigated. By systematically varying the most important parameters, we will investigate the optimal settings of noise reduction algorithms.