Abstract
Background. The aim of this study was to investigate the individual effects of envelope enhancement and high-pass filtering (500 Hz) on word identification scores in quiet for individuals with Auditory Neuropathy. Method. Twelve individuals with Auditory Neuropathy (six males and six females) with ages ranging from 12 to 40 years participated in the study. Word identification was assessed using bi-syllabic words in each of three speech processing conditions: unprocessed, envelope-enhanced, and high-pass filtered. All signal processing was carried out using MATLAB-7. Results. Word identification scores showed a mean improvement of 18% with envelope enhanced versus unprocessed speech. No significant improvement was observed with high-pass filtered versus unprocessed speech. Conclusion. These results suggest that the compression/expansion signal processing strategy enhances speech identification scores—at least for mild and moderately impaired individuals with AN. In contrast, simple high-pass filtering (i.e., eliminating the low-frequency content of the signal) does not improve speech perception in quiet for individuals with Auditory Neuropathy.
Highlights
Conventional hearing aids amplify acoustic signals to make sounds audible to hearing-impaired individuals
The improvement observed for envelope-enhanced speech ranged from 8% to 36% with a mean improvement of 18.3%
To assess effect of gender on identification scores in unprocessed and envelope-enhanced condition, a paired sample “t” test was performed and results showed no significant effect of gender on identification for unprocessed (t = 0.44, P = 0.66) and envelope-enhanced (t = −0.31, P = 0.75)
Summary
Conventional hearing aids amplify acoustic signals to make sounds audible to hearing-impaired individuals. The first scheme is the linear amplification, in which a set amount of gain is applied to the input signal In this design, the maximum output is limited by peak clipping, which causes various forms of distortion and reduces the intelligibility and subjective quality of speech. Amplitude compression is implemented by an analog circuit or by a digital processing algorithm to reduce the gain of the instrument when either the input or output exceeds a predetermined level [1] This type of amplification results in a wider dynamic range, making soft sounds audible without making loud sounds uncomfortably loud [2]. These results suggest that the compression/expansion signal processing strategy enhances speech identification scores—at least for mild and moderately impaired individuals with AN. Simple high-pass filtering (i.e., eliminating the low-frequency content of the signal) does not improve speech perception in quiet for individuals with Auditory Neuropathy
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