Tutorial paper:principles and characteristics of automatic gain control hearing aids.

Among the available auditory rehabilitative resources, automatic gain control (AGC) hearing aids comprise a unique class of personal amplifying systems. They are unique because of their capability of achieving some degree of self-regulation. However, partly due to the standard methods of portraying and describing electroacoustic data for conventional (non-AGC) aids, certain characteristics of AGC aids, such as are related to signal and noise relations over time, seem to be commonly unappreciated by the typical clinician. This paper discusses some principles of amplifying behavior that are common to all AGC hearing aid systems, as well as various design modifications. The ramifications of these properties are pointed out with a view towards greater clinical implementation of the available technology.