Unfortunately, a hearing aid will never be able to accomplish the sifting and sorting that is carried out in the human brain. While a person with normal hearing sits in a restaurant, he can distinguish a conversational speech signal that is as little as three decibels greater than the ambient noise. On the other hand, a person with a 30-decibel sensorineural loss might need the speech signal to be 15 or more decibels greater than the ambient noise. The hearing aid's task is to acoustically or electronically compensate for both the neurological shortcomings of the hearing impaired person and the wide band increase inherent in any basic amplifier.
Acoustic compensation can be carried out in a hearing aid microphone. Most hearing aids today utilize omnidirectional microphones, which pick up sound equally from all directions. This may be beneficial and practical in some cases, as in the completely in the canal (CIC) aid. The CIC aid uses the natural funneling of the auricle in order to focus sound directly into the instrument. Behind-the-ear (BTE) and full concha in-the-ear (ITE) aids lose this anatomical feature, and may benefit from a directional microphone. "The purpose of using a directional microphone is to focus its sensitivity toward the front of the listener, thereby attenuating or reducing unwanted "noise" or competition emanating from behind the listener." (Stach 1998)
Microphone directionality can be... [continues]
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(1999, 10). Noise Reduction in Hearing Aids. StudyMode.com. Retrieved 10, 1999, from http://www.studymode.com/essays/Noise-Reduction-Hearing-Aids-10691.html
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