Strategies for enhancing the consonant to vowel intensity ratio with in the ear hearing aids

Numerous investigators have suggested that increasing the consonant to vowel intensity ratio (CVR) may improve speech intelligibility. This investigation was designed to determine the extent to which analog circuits, small enough to fit into in the ear hearing aids, can increase the CVR, and whether CVR enhancement is of benefit to hearing-impaired listeners. Real ear CVRs, calculated from real ear recordings of nonsense syllables, were obtained from eight hearing-impaired listeners. Recordings from each listener were obtained through each of four hearing aid circuits: (1) an adaptive high-pass filter; (2) a faster acting adaptive high-pass filter; (3) the fast-acting adaptive high-pass filter with expansion; and (4) an infinite amplitude clipper. The amount of CVR enhancement was compared to performance of the subjects with a NST speech recognition task. Subjects also ranked the four circuits for amount of consonant emphasis provided. Results indicated that the four hearing aid circuits increased the real ear CVR by 4 to 6 dB, relative to unaided. Aided CVR varied, however, across circuits and between fricative and stop consonants. Performance on the NST recognition task was generally consistent with the amount of CVR increase provided. Rank ordering for consonant emphasis was consistent with aided CVR for stop consonants, but not for fricatives.