Effects of single-channel phonemic compression schemes on the understanding of speech by hearing-impaired listeners

The effect of digital processing on speech intelligibility was studied in h earing-impaired listeners with moderate to severe high-frequency losses. Th e amount of smoothed phonemic compression in a high-frequency channel was v aried using wide-band control. Two alternative systems were tested to compe nsate for upward spread of masking (USOM) and to reduce modulations in the high-frequency channel effectively. Consonant-vowel-consonant tests were co nducted in a group of 14 subjects using eight different speech-processing s ettings. Speech intelligibility improved significantly with compression, ma inly due to positive effects on the initial-consonant score. Surprisingly, listeners with a smaller residual dynamic range tended to profit less from compression. Compensation for USOM gave an additional improvement of vowel intelligibility. In background noise, consistently negative effects of spee ch processing were found. The combined use of phonemic compression and USOM compensation is promising in conditions without background noise.