Hearing Aids—A Review of Past Research on Linear Amplification, Amplitude Compression, and Frequency Lowering. (ASH A Monographs Number 19)

The auditory system allows the estimation of the distance to sound-emitting objects using multiple spatial cues. In virtual acoustics over headphones, a prerequisite to render auditory distance impression is sound externalization, which denotes the perception of synthesized stimuli outside of the head. Prior studies have found that listeners with mild-to-moderate hearing loss are able to perceive auditory distance and are sensitive to externalization. However, this ability may be degraded by certain factors, such as non-linear amplification in hearing aids or the use of a remote wireless microphone. In this study, 10 normal-hearing and 20 moderate-to-profound hearing-impaired listeners were instructed to estimate the distance of stimuli processed with different methods yielding various perceived auditory distances in the vicinity of the listeners. Two different configurations of non-linear amplification were implemented, and a novel feature aiming to restore a sense of distance in wireless microphone systems was tested. The results showed that the hearing-impaired listeners, even those with a profound hearing loss, were able to discriminate nearby and far sounds that were equalized in level. Their perception of auditory distance was however more contracted than in normal-hearing listeners. Non-linear amplification was found to distort the original spatial cues, but no adverse effect on the ratings of auditory distance was evident. Finally, it was shown that the novel feature was successful in allowing the hearing-impaired participants to perceive externalized sounds with wireless microphone systems.

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Effects of Linear Amplification and Amplitude Compression on Sentence Reception by Listeners With Hearing Loss Simulated by Masking Noise

Modeling Sensorineural Hearing Loss ◽

10.4324/9781315789392-11 ◽

2019 ◽

pp. 131-147

Author(s):

Steven V. De Gennaro ◽

Louis D. Braida

Keyword(s):

Hearing Loss ◽

Linear Amplification ◽

Masking Noise ◽

Amplitude Compression

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Review of Recent Research on the Selection of Frequency-Gain Characteristics for Hearing Aids

Annals of Otology Rhinology & Laryngology ◽

10.1177/00034894800890s522 ◽

1980 ◽

Vol 89 (5_suppl) ◽

pp. 79-83

Author(s):

Richard Lippmann

Keyword(s):

Hearing Aids ◽

Speech Intelligibility ◽

Signal To Noise Ratio ◽

Hearing Aid ◽

Linear Amplification ◽

Percentage Points ◽

Gain Characteristic ◽

The Relationship ◽

Fitting Hearing Aids ◽

Selection Of

Following the Harvard master hearing aid study in 1947 there was little research on linear amplification. Recently, however, there have been a number of studies designed to determine the relationship between the frequency-gain characteristic of a hearing aid and speech intelligibility for persons with sensorineural hearing loss. These studies have demonstrated that a frequency-gain characteristic that rises at a rate of 6 dB/octave, as suggested by the Harvard study, is not optimal. They have also demonstrated that high-frequency emphasis of 10–40 dB above 500–1000 Hz is beneficial. Most importantly, they have demonstrated that hearing aids as they are presently being fit do not provide maximum speech intelligibility. Percent word correct scores obtained with the best frequency-gain characteristics tested in various studies have been found to be 9 to 19 percentage points higher than scores obtained with commercial aids owned by subjects. This increase in scores is equivalent to an increase in signal-to-noise ratio of 10 to 20 dB. This is a significant increase which could allow impaired listeners to communicate in many situations where they presently cannot. These results demonstrate the need for further research on linear amplification aimed at developing practical suggestions for fitting hearing aids.

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