Speech Intelligibility Improvement based on Noise Reduction and Frequency Compression Technique

Abstract

A combined structure of noise reduction and multi band frequency compression (MFC) technique has been developed to compensate for the spectral masking effect in people with sensorineural hearing impairment. Increased spectral masking reduces the speech intelligibility that affects the speech perception especially under adverse listening conditions. Noise reduction techniques namely wiener filter and spectral subtraction methods have been used in the combined structure to reduce background noise. To quantify the intelligibility of perceived speech, listening test using Modified Rhyme Test (MRT) was conducted for normal hearing and hearing impaired persons in the presence of additive noise. Test material consists of 300 words. Each word starts with phrase “would you write——”. Results of MRT, when processed by cascading wiener filter with a MFC scheme, for the compression factor of 0.6 conducted on hearing-impaired subjects suggest improvement in speech intelligibility of 25.92%, to 30.134 % and decrease in response times of 0.815 to 1.626 seconds for SNR values of +6 dB to - 6 dB in periods of +3 dB respectively. For spectral subtraction technique when cascaded with MFC scheme, an improvement in speech intelligibility of 20.22 % to 25.804 % and decrease in response times of 0.452 to 0.995 seconds for SNR values of +6 dB to - 6 dB in periods of +3 dB respectively. The results of this study showed an improvement in speech intelligibility and a reduction in the load of perception.