Functional gain.
The concept of functional gain was popularized by Pascoe in 1975, and for some time was one of the most popular hearing aid evaluation techniques. More recently probe tube systems for measuring insertion gain have become popular, and some questions regarding the continued utility of functional gain have been raised. In this paper some of the major advantages and disadvantages of functional gain are reviewed. While functional gain is subject to contamination from noise external or internal to the hearing aid, it does provide subjective information not available from insertion gain.
Acoustics↗