Acoustic Analysis of the Speech Processed Through Three Amplification Strategies and Their Effect on Speech Recognition Scores of Individual with Severe Hearing Impairment

Abstract

Individuals with severe hearing impairment exhibit reduced frequency resolution and temporal discrimination. Therefore the requirements of amplification for this group of population will be different from those with lesser degree of hearing loss. The aim of the present study was to investigate acoustic changes to the speech signal [in terms of Consonant Vowel Ratio (CVR) and Envelope Difference Index (EDI)] that occurred with different amplification strategies and to examine the relationship between such changes and speech perception in individuals with severe sensorineural impairment. A total of 10 subjects having moderately severe to severe hearing loss participated in the study. Speech Recognition Scores were calculated for CV nonsense syllable list at input level of 65 and 80 dBSPL for the three amplification strategies viz Peak Clipping, Compression Limiting, and Wide Dynamic Range Compression. Consonant Vowel Ratio was calculated for the unprocessed and processed stimuli for 5 subjects and Correlation Index for one subject at input level of 65 and 80 dBSPL for all the three strategies using Matlab software. The scores were better with Compression Limiting compared to Wide Dynamic Range Compression (WDRC) at both 65 and 80 dBSPL. The CVR values for the processed stimuli with vowel environment /u/ were higher for the Compression Limiting strategy as compared to WDRC and at 65 and 80 dBSPL for /a/ and /i/ at 80 dBSPL. The EDI value was greater at 65 dBSPL and as the level increased to 80 dBSPL there was a decrease in the EDI value for all the three strategies. The results of the present study indicate a relationship between acoustic changes to the hearing aid processed speech signal and speech perception performance of severely hearing impaired individuals.