Frequency shaping and multiband compression in hearing aids

Compression and noncompression amplification were compared for a range of conditions. The noncompression conditions included flat-frequency response and “LDL frequency response,” with and without peak clipping. The compression conditions included a single-band compression system and two combinations of a two-channel compression system. The LDL frequency response was obtained by finding the LDL for each subject using one-third octave bands of noise and then determining that frequency response which would amplify each one-third octave band of speech to just below the LDL for that band. A low-frequency roll off below 300 Hz was used to reduce upward spread of masking. Four hearing-impaired persons served as subjects. Four replications of the Nonsense Syllable Test were administered in quiet and in noise for each experimental condition. The highest scores were obtained, on the average, for the condition of noncompression, no peak clipping, with the LDL frequency response. There were, however, large individual differences in relative performance on different conditions, indicating the importance of individualized determination of optimum amplification characteristics.