# Advanced Hearing Aid Services

Adaptive Feedback Cancellation
Acoustic feedback (whistling from the hearing aid) can be annoying, embarrassing, and in some cases, prevent the hearing aid wearer from using the correct amount of gain. Many of today's hearing aids have an automatic feature that quickly detects acoustic feedback and cancels it. This feature is designed to manage transitory feedback (e.g., caused by placing one's hand or a telephone next to the ear), and is not a solution to a poorly fitted ear mold or hearing aid. Although feedback can be managed it can never be eliminated completely no matter the hearing aid.
Automatic Gain Control
AGC or compression is used to put a "ceiling" on loud sounds. Compression allows for soft, medium, and loud sounds to be programmed individually without any sound being too loud. The AGC also allows for most individuals to not worry about adjusting the volume on the hearing aid as the hearing aid will automatically adjust volumes in different environments, similar to a normal hearing ear.
Digital Noise Reduction
With digital hearing aids, it is possible for the hearing aid to analyze an incoming signal and differentiate speech from a noise signal. If the dominant signal is noise , there is a reduction in gain while still helping to preserve audibility of speech. Note, however, that what a typical hearing aid user might consider to be"noise," (background talkers at a party) might not be considered "noise" by the hearing aid.
Digital Signal Processing
Until recently, the majority of hearing aids utilized analog signal processing. This has changed rapidly the past few years, and today, nearly all hearing aids sold in the U.S. utilize digital signal processing. The advantage of digital processing is that less space is required, allowing manufacturers to include many more"programmable features" in a small package. Through the use of digital signal processing, the hearing aid
can conduct an analysis of an incoming signal, and make a reasonable classification of the content-speech versus broad-band noise versus acoustic feedback (whistling) versus music, for example. This classification can then be used to trigger automatic activation of other special features.
Directional Microphone Technology
Using special microphones or phase cancellation signal processing, it is possible to configure a hearing aid so that sounds from the side, and especially the back of the hearing aid user are amplified less than sounds originating from the front. It can serve as a type of noise reduction if the user is correctly positioned. Directional technology is available on all hearing aid styles except CICs (because of size constraints). Importantly, directional technology does not improve localization of sounds. Research has shown that many hearing aid users prefer directional technology for listening in noise. Some hearing aids automatically switch to a directional mode when noise is detected. Adaptive directional hearing aids automatically tracks a dominant single noise source (e.g., a car passing by someone on a sidewalk), attempting to provide maximum reduction in gain toward the location of the source.
Multiple Channels
The majority of today's hearing aids have multiple channels. Each channel represents a portion of the frequency range important for understanding speech. One advantage of multiple channels is that features such as gain and compression can be programmed differently to reflect changes in the patient's hearing across frequencies. Multiple channels also are useful for implementing other features such as digital noise reduction and feedback cancellation.
Telecoils
With this special circuit, electromagnetic signals can be picked up from the handset of the telephone and amplified in a manner similar to the amplifying function of the hearing aid. Many hearing aid wearers report benefit with this circuit. Telecoils are not available in some smaller custom-made models due to space limitations. Often, hearing aids with multiple memories will devote one memory to the telecoil. In these instruments, the Telecoil can be accessed through a push button on the hearing aid or by the use of a remote control.
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