Frequency Compression and Transposition

Hearing aids are designed to help overcome some of the communication challenges faced by individuals with hearing loss. The primary function of a hearing aid is to amplify soft sounds, especially speech sounds, so that they are audible. Hearing-impaired individuals have less difficulty hearing loud sounds, so hearing aids must also turn down the amplification as the sound level increases. In addition, because hearing loss usually varies across the frequency range—generally worsening as the sound frequency increases—the amplification characteristics must also vary across the frequency range. This means that high-frequency speech sounds, such as [s], [f], and [T], which are some of the softest speech sounds in the English language and in most other languages, need a lot of amplification to overcome the severity of ...