Gain (Hearing Aid)
Gain, in the context of hearing aids, refers to the amount of amplification the device adds to an incoming sound. It is measured in decibels and represents the difference between the sound level entering the microphone and the sound level delivered to the ear canal. If a sound enters the hearing aid at 60 dB and the device delivers 80 dB to the ear, the gain is 20 dB.
Hearing aids do not apply the same gain to all sounds or at all frequencies. A well-fitted hearing aid applies more gain where hearing loss is greatest and less gain where hearing is closer to normal. Prescriptive fitting formulas such as NAL-NL2 and DSL calculate the target gain from the individual's audiogram. Real ear measurement (REM) is used to verify that the gain actually delivered in the ear canal matches this prescribed target.
Too much gain causes discomfort, distortion, and feedback. Too little gain leaves the person under-amplified. Striking the right balance across frequencies requires both the prescriptive formula and in-situ verification.
