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. 1. Introduction Conventional hearing aids amplify acoustic signals to make sounds audible to hearing-impaired individuals. Their basic structure consists of a microphone, an amplifier, a receiver (speaker), and a power supply. The amplifier is the major component that amplifies the input signal. Two types of amplification schemes are typically used in hearing aid design. 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. The second scheme is a nonlinear amplification, which reduces gain as the output or input approach maximum values. In this scheme, 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]. However, amplitude compression also changes the temporal properties of the original speech signal, which may reduce speech intelligibility. Conventional hearing aids are not effective for all hearing impairments [3, 4]. The primary function of a conventional hearing aid is to amplify and make the speech signal
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