How do you use "expansion" when fitting?
Expansion only acts on sounds that are lower than the expansion kneepoints. This means that if the hearing aid user complains about noise in noisy surroundings, when driving, when others are talking, or when watching TV, expansion will not have any impact. On the other hand, if an individual reports that she hears a soft hissing noise when in a quiet room, turning on or increasing the level of expansion can alleviate this complaint.
You might wonder why expansion is not just set to the strongest setting per default. The reason for this is that the expansion kneepoints are high enough that they may overlap with very soft speech sounds. Since the main goal of the ReSound fitting strategy is increased audibility of these sounds, the expansion level is typically set to "Mild" for most fittings. However, the Aventa fitting software provides the clinician with the flexibility to increase this level, if it is an acceptable trade-off for potentially reduced audibility for the individual patient.
A unique aspect of expansion in the ReSound Alera is that the kneepoints are device-dependent. For each type of device, electroacoustic analysis included careful measurements of the instrument noise floor. Expansion kneepoints were then set to be above the level of the instrument noise floor. This is in contrast with most expansion algorithms, which define kneepoints at fixed levels below the WDRC kneepoints regardless of the device noise floor. The problem with using a fixed expansion level for all devices is that for devices with a higher noise floor, such as power BTEs, expansion may have little effect, while devices with a low noise floor may have too much expansion and subsequent gain reduction. Thus, the device-dependent ReSound approach ensures that expansion is effective for each device type.
Tammara Stender, Au.D., CCC-A is a Senior Audiologist at GN ReSound, where she plans and conducts clinical trials for newly developed hearing aid technology and prepares documentation for released products. Her research interests include hearing aid benefit and satisfaction, the occlusion effect and spatial localization abilities with hearing aids. She received her Master of Science degree from Vanderbilt University, and her Doctor of Audiology degree from the University of Florida.
Learn more about ReSound at www.gnresound.com or on the ReSound web channel