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Brief Guide To Modern Hearing Instrument Technology

In addition to the basic features of hearing instruments, there are many other features available in modern hearing instruments – some of them are for convenience and ease of use, others are designed to improve speech understanding or listening comfort.

Adaptive Feedback Cancellation: Acoustic feedback (whistling from the hearing instrument) can be annoying, embarrassing, and in some cases, prevent the hearing instrument wearer from using the correct amount of gain. Many of today’s hearing instruments 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 instrument.

Automatic Gain Control – Output (AGCo):  AGCo or output compression is used to put a “ceiling” on loud sounds. It handles the output after the amplifier, and can be adjusted to correspond to the patient’s threshold of discomfort (maintaining sounds below this level).

Automatic Gain Control – Input (AGCi):  AGCi, or input compression, often referred to wide dynamic range compression (WDRC) is used to “repackage” the speech signal (and other incoming sounds) to correspond to the reduced dynamic range of the hearing instrument user. That is, if the incoming sounds have a 60 dB range, and the patient only has a 30 dB range of useful hearing, the sounds might be “compressed” by 2:1 to fit into the useful auditory region. The notion is that most people with a hearing loss need more gain for soft sounds than for average, and more gain for average sounds than for loud. WDRC accomplishes this automatically – in fact, if the WDRC is programmed correctly across frequencies, many hearing instrument users have little need for a volume control.

Digital Noise Reduction:  With digital hearing instruments, it is possible for the hearing instrument to analyze an incoming signal and differentiate speech from a broad-band noise signal. This can be accomplished simultaneously in several channels. If the dominant signal is believed to be noise in a given channel, there is a reduction in gain. Note, however, that what a typical hearing instrument user might consider to be “noise”, (background talkers at a party) might not be considered “noise” by the hearing instrument. While this feature has the potential to improve speech understanding in typical difficult listening situations, this has yet to be verified by research.

Digital Signal Processing:  Until recently, the majority of hearing instruments utilized analog signal processing. This has changed rapidly over the past few years, and today, nearly all hearing instruments 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 instrument 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 instrument so that sounds from the side, and especially the back of the hearing instrument user are amplified less than sounds originating from the front. It can serve as a type of “spatial” noise reduction if the user is correctly positioned. Directional technology is available on all hearing instrument styles except CICs (because of size constraints). Importantly, directional technology does not improve localization of sounds. Research has shown that many hearing instrument users prefer directional technology for listening in noise, usually when:

  • The noise originates from behind the listener,
  • The talker is in front of the listener,
  • The listener is close to the talker,
  • The room has low reverberation.

Some hearing instruments automatically switch to a directional mode when the signal type and/or input intensity are matched to the characteristics of the algorithm. Adaptive directional hearing instruments automatically track 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 instruments 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. There is no consensus regarding how many channels are enough (or how many are too many) – to some extent, this depends on the feature utilized within the channels.

Hearing Instruments

Multiple Memories:  A memory is a location to store hearing instrument settings that are designed for a particular listening situation. It is common for hearing instruments to have two or three memories. For example, in a hearing instrument with three memories, it is common that memory one will be for listening in quiet, memory two will be for listening in noise, and memory three will be for telephone. On the other hand, many hearing instrument users find that a single memory works in a variety of listening situations, and may only use one memory. Changing memories is accomplished by using a button (or toggle switch) on the hearing instrument, with a remote control device. In some digital hearing instruments, it happens automatically.

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 instrument. Although many hearing instrument wearers report benefit with this circuit, there is substantial variability across hearing instruments. Telecoils are not available in some smaller custom-made models due to space limitations. Often, hearing instruments 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 instrument or by the use of a remote control device.

The Binaural Advantage (Two are better than one)

If you have hearing loss in both ears (bilateral hearing loss), then most likely you are a candidate for two hearing instruments. While a hearing healthcare professional can determine best if you are a candidate for two hearing instruments, the ultimate decision-maker concerning binaural instruments is the person who will wear them. It is important that the person with the hearing loss be given the chance to experience binaural (two hearing instruments) amplification, before a decision on one or two hearing instruments is made. Similar to the way refractory problems in both eyes are treated with a pair of glasses, it makes sense that bilateral hearing loss should be treated with binaural hearing instruments.

Let me share with you why two hearing instruments are better than one (visit www.betterhearing.org for more detailed explanations of the binaural advantage):

  • Better understanding of speech
  • Better understanding in group and noisy situations
  • Better ability to tell the direction of sound
  • Better sound quality
  • Smoother tone quality
  • Wider hearing range
  • Better sound identification
  • Keeps both ears active resulting in potentially less hearing loss deterioration
  • Hearing is less tiring and listening more pleasant
  • Feeling of balanced hearing
  • Greater comfort when loud noises occur
  • Reduced feedback and whistling
  • Tinnitus (ringing in the ears) masking
  • Consumers prefer two over one
  • Customer satisfaction is higher with two

Logically, just as you use both eyes to see clearly, you need two healthy ears to hear clearly. Before you decide on one hearing instrument, try two. Your hearing healthcare professional can demonstrate to you the binaural advantage experience either through headphones (during testing), probe microphones, master hearing instruments, or during your trial fitting. Decide for yourself. 


Harris HEB Center
1615 Hospital Parkway, Suite 210
Bedford, Texas 76022
Ph: 817-540-3121  FAX: 817 355-4532
Business Office Location
Baylor Grapevine Professional
Office Building
1600 W. College Ave., Suite 270
Grapevine, Texas 76051
Ph: 817-540-3121   FAX: 817 421-6728
Watermere Medical Plaza
2813 W. Southlake Blvd.
Southlake, Texas 76092
Ph: 817-421-6700
FAX: 817 421-6757