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Sensorineural hearing loss which occurs due to the damage of cochlea, auditory nerves or both, is characterized by elevated hearing threshold, loudness recruitment, reduced temporal and frequency resolution, and increased temporal and spectral masking. Increased temporal masking affects the speech perception in persons with sensorineural hearing impairment especially under adverse listening conditions. Hearing aid users have problem in speech understanding particularly in the presence of background noise. Hence hearing aids should include noise reduction techniques for enhancing the speech perception. This paper presents a cascaded scheme, which employs a noise reduction algorithm as well as temporal splitting of the speech signal. The main objective of the paper is to improve quality of perceived speech for SNHL listeners by reducing the temporal masking and improve the speech perception in the background of additive noise. Earlier investigations have shown that by splitting the speech temporally and presenting alternate segments to the two ears help in reducing the effect of temporal masking. In this technique, the speech signal is processed by two fading functions, complementary to each other, and presented to left and right ears for binaural dichotic presentation. In the present study, half cosine signal is used as fading function with crossover gain of 6 dB for perceptual balance of loudness. Temporal splitting is combined with noise reduction algorithm to improve speech perception in the background noise. Two noise reduction schemes, namely spectral subtraction and Wiener filter are used. We have used Voice Activity Detection (VAD) based on short term energy and zero crossing rates to detect noise and speech frames separately. Listening tests were conducted on six normal hearing subjects, with sensorineural loss simulated by adding broadband noise to the speech signal at different signal-to-noise ratios (∞, 3, 0, and -3 dB). Objective evaluation using PESQ was also carried out. The MOS score for VCV syllable /asha/ for SNR values of ∞, 3, 0, and -3 dB were 5, 4.46, 4.4 and 4.05 respectively, while the corresponding MOS scores for unprocessed speech were 5, 1.2, 0.9 and 0.65, indicating significant improvement in the perceived speech quality for the proposed scheme compared to the unprocessed speech.
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