The objective and subjective evaluation of low-frequency expansion in wide dynamic range compression hearing instruments.

The effects of low-frequency expansion on the objective and subjective evaluation of four channel in-the-ear hearing instruments was investigated. Three expansion settings were programmed in each device: expansion off, expansion restricted to channel one, and expansion restricted to channels one and two. Objective evaluations were conducted in quiet (Connected Speech Test) and in noise (Hearing in Noise Test) with speech levels fixed at 40 dB SPL. Subjectively, each participant rated expansion satisfaction in quiet and listening to low-level speech in a sound-treated room then indicated the expansion condition preferred overall. Listeners performed significantly better in quiet and in noise for the Off and Channel 1 conditions than the Channels 1 and 2 condition; however, performance was similar between the Off and Channel 1 conditions. Expansion effects on listener satisfaction ratings depended on the listening environment. Overall, listeners preferred expansion in Channel 1 to expansion in Channels 1 and 2; however, preference was not significantly different between the Channel 1 and Off conditions. Results indicate restricting expansion to 1000 Hz overcomes speech-recognition deficits observed with expansion active across a broader spectrum without significantly reducing subjective benefit or preference.