Selecting Compression Thresholds for Automation of Volume Control in Single Channel Programmable Aids: Results of Two Field Studies Christopher Barker Australian Hearing has issued more than half a million Bernafon/NAL programmable hearing aids since 1993. These fast-acting single channel programmable aids are capable of being fitted with a variety of input/output characteristics: linear with peak clipping; linear with compression limiting; filter independent Wide Dynamic Range Compression (WDRC) with a 2:1 compression ratio; filter dependent WDRC, and expansion ("soft squelch"). Learning when to apply which configuration and at what level(s) has been the subject of several NAL research projects. This poster session outlines the results of a field study into the selection of compression threshold for the 2:1 AGCi circuit in the filter independent mode. Field trials were undertaken by 32 adults with mild through to profound losses. Results indicated that for most subjects 2:1 AGCi at higher levels (60 dB SPL+) provides benefits over and above linear amplification and filter independent WDRC. A reduction in the need for manual volume control adjustment, enhanced comfort in higher level noise, acceptable levels of internal and external ambient noise all contributed to a significant preference for this option over WDRC and linear amplification for the majority of subjects. High levels of satisfaction in multiple listening situations were reported, suggesting that some degree of nonlinearity would be appreciated by a large percentage of the aided hearing impaired. |