The Objective and Subjective Evaluation of Multichannel Expansion in Wide Dynamic Range Compression Hearing Instruments

Abstract

The effects of multichannel expansion on the objective and subjective evaluation of 20 listeners fitted binaurally with 4-channel, digital in-the-ear hearing instruments were investigated. Objective evaluations were conducted in quiet using the Connected Speech Test (CST) and in noise using the Hearing in Noise Test (HINT) at 40, 50, and 60 dB SPL. Subjective evaluations were conducted by having each participant (a) rate their satisfaction regarding the amount of noise reduction they perceived daily and (b) indicate which expansion condition they preferred overall after a 2-week trial. Three expansion settings were programmed into the hearing aids: 4-channel expansion, expansion restricted to Channels 1 and 2 only, and expansion off. Listeners performed significantly better in quiet (CST) and in noise (HINT) for the off condition than for either multichannel condition; however, restricting expansion to Channels 1 and 2 improved objective performance in quiet and in noise relative to the 4-channel condition. Conversely, satisfaction ratings were significantly greater for both multichannel conditions than for the off condition; however, satisfaction ratings were similar for the restricted and the 4-channel conditions. Overall, listeners preferred any form of multichannel expansion to no expansion; however, overall preference was similar for the restricted and the 4-channel conditions. Hearing instrument users prefer the use of multichannel expansion despite the fact multichannel expansion may significantly reduce the recognition of low-level speech in quiet and in noise. Although restricting expansion to Channels 1 and 2 (i.e., 2000 Hz and below) maintained subjective benefit for wide dynamic range compression hearing instrument users, the recognition of low-level speech was not completely preserved.