Digital Versus Analog:
Digital technology is the most sophisticated hearing aid technology. Digital technology gives the hearing professional control over sound quality and sound processing characteristics.
Analog technology is comprised of a basic amplifier with a relatively fixed frequency response and very limited features. Some patients with a long history of hearing aid use will still request this technology due to the nature of how the sound is processed. Usually, these patients have a more severe hearing loss and enjoy the perceived loudness he or she had experienced with the older aids and look to duplicate it. With the limited availability and adjustability of analog instruments it is actually more practical to try to duplicate the sound quality with a digital hearing aid rather than an analog one. Using our speech mapping and aural rehabilitation, the benefits of transitioning to digital technology are usually quickly appreciated by even the most skeptical user.
In addition to the basic features of hearing aids discussed, there are many other features available in modern digital hearing aids. Some of them are for convenience and ease of use while others are designed to improve speech understanding or listening comfort. Below is a brief outline of some of the key features of digital hearing aids.
Most digital hearing aids have an automatic feature which can quickly detect acoustic feedback and immediately eliminate it. This whistling from the hearing aid would normally be annoying, embarrassing, and may even prevent the hearing aid wearer from benefiting from appropriate amounts of gain. This feature has been paramount in the advancement of hearing aids and their performance by allowing the development of open-fit hearing aids which have virtually eliminated the occluded feeling. Feedback cancellation also allows the user to use the phone with greater ease for even greater user satisfaction.
Automatic Gain Control (AGC):
Automatic gain control is probably the most distinguishing characteristic of the digital hearing aid. From the point of when a sound is first processed to the level of output to the user’s ear, the action of the AGC is always working. The easiest way to grasp its purpose is to realize the primary purpose of a hearing aid; make soft sounds audible, medium sounds comfortable, and loud sounds tolerable according to the user’s residual hearing ability. All of this is done in each independent channel at a predetermined level according to the individual hearing loss prescribed for each ear and the individual’s perception of overall sound quality! The AGC also controls the levels of sound in relation to feedback suppression, noise reduction, speech enhancement, and output limiting. When one keeps in mind the speed at which this feat is being accomplished, it is easy to be in awe of these little devices and appreciate how far this industry has come. We essentially have a personal “sound system” reconfiguring the entire array of incoming sounds and delivering them to the reduced dynamic range of the impaired human auditory system.
Many digital hearing aids have a noise reduction feature which makes it possible to monitor and suppress background noises across numerous individual channels. As an incoming signal is analyzed, the noise reduction feature distinguishes whether it is speech or noise based on the characteristics of the signal. Sound with little modulation across a narrow frequency range (such as a fan or dishwasher) is treated as noise and thus given a reduction of gain to allow the speech signal to be emphasized and heard more dominantly. While this feature works well in many situations, it should be noted that in some situations, such as a party, the characteristics of the noise may be similar to everyday speech and is not the predominant means to helping the user communicate in this type of environment. Incorporating directional microphones is the most effective way to enhance speech and reduce noise this this difficult listening environment.
Speech enhancement is also available in many advanced digital hearing aids, and works essentially the opposite as noise reduction. As an incoming signal is analyzed, if it is determined to have modulation and frequency characteristics similar to speech, it gets enhanced in the ranges most relevant for the user to get more clarity of the speech sounds. While incorporating this feature with directional microphones, it can become a useful tool in adding clarity while in the presence of background noise.
Directional Microphone Technology:
Directional microphones are the only technology which has been proven to enhance the signal (speech) in noise ratio. These tiny dual microphones are available on nearly all hearing aid models and styles with the exception of the completely-in-canal (CIC) hearing aids (due to size constraints). At the most basic level, directional microphones will enhance sounds from in front of the listener more than the sounds originating from behind. Because of the successes achieved from this technology, most manufacturers have worked vigorously to enhance the performance of this technology. Adaptive directionality is allowing people to get an enhanced sound from different directions, and noise reduction from a moving source (user does not have to face the signal). Some sound localization is also being realized with directional microphones. With the advent of wireless technology, the dual microphones from one hearing aid can “team up” with the microphones of the hearing aid on the opposite ear to further determine sound characteristics for advanced sound processing. With some automatic hearing aids, the program changes of the instruments may turn the directional mode on or off in response to presence of background noise. Regardless of the level of technology of your hearing aids, directional microphones should not be overlooked. The following guidelines should always be practiced by the user when trying to get the most from the hearing aids in the most difficult listening environments.
- Separate the signal (speech) from the noise as much as possible,
- Keep the speaker in front of you and the noise behind you,
- Be in close proximity the speaker,
- Make sure your hearing aids are in a directional mode.
If your hearing aids are not automatic, be sure to change back to the program which allows for regular listening in a quiet environment. Although while listening in the directional mode may seem like a pleasant sound quality, you will quickly realize the sharpness and clarity in this mode will not be realized when trying to listen at a distance in a quiet environment.
Channels and Bands:
Over the years, there has been some confusion about bands and channels within a hearing aid. Both of the terms describe performance of the hearing aid as it relates to the frequency (or pitches) of the sounds being processed. The easiest way to understand the difference is to visualize an equalizer often used in a standard audio system and consider that a band. These little “sliders” can enhance various frequency ranges independently to give an optimum level of gain according to the individual’s hearing loss or preferred listening level. Although a band might be equal to one channel, that is not always the case. There may be two or more bands in any given channel. Herein lays the difference. A channel will process the sound in a distinct manner without having an effect on any other channel, but could affect multiple bands. When a hearing aid goes into compression or when the noise reduction feature reduces gain in any given channel (including feedback management), it will not affect any of the other channels. Your hearing instrument specialist will be able to help you decide which combination of numbers of bands and channels will work best for you and your hearing loss, but don’t be led to believe these two terms are one in the same.
Memories or Programs:
A memory is a setting programmed into a hearing aid. While a primary memory works well a majority of the time, a hearing aid user will often express there are times when it is difficult to hear in different listening environments. With a user control (remote control, pushbutton, or switch), it is possible to change the programming of the hearing aid to an entirely different setting. After the user leaves the area where the difficulty exists, he or she can quickly revert back to the primary program which has worked so well before. For example, a user may do quite well listening in his or her own home when there is control over the level of noise in the environment, but the hearing aids are too loud when having dinner at a favorite restaurant. When changing to a different memory, the gain, compression, directional microphones, noise reduction, and other characteristics of the hearing aids can be optimized for the particular environment where the difficulty exists, in this case the restaurant. These programs are generally predefined for listening in quiet, listening in noise, comfort in noise, music, and for the telephone, but can also be tweaked to individual requirements. Since everyone has his or her own lifestyle, I have programmed hearing aids to adapt to such things as playing tennis, archery hunting, bowling, riding ATV, demanding work environments, and even simple volume adjustments when a volume control was not available. It should also be noted that some digital hearing aids have an automatic programming adjustment (based on the environment) which will make these adjustment for the user without user intervention.
T-coils are often one of the least understood and underutilized features of a hearing aid. This feature is usually activated with a user controlled switch, but can also be activated automatically in some models simply by placing a phone near the hearing aid. Hearing aids equipped with T-coils use a special electro-magnetic “coil” which is positioned inside the hearing aid. The handset on most telephone receivers is also equipped with a similar such device. When the two magnetic coils are placed within close proximity of each other, a signal from the telephone receiver is transmitted to the hearing aid and processed (amplified) according to the user’s needs. There are few key points that should be made for a user to get the benefit from this key feature.
- This is not the “OFF” position! Since the use of the T-coil will often shut off the hearing aid microphones, many users report that the hearing aid is no longer working when this program is engaged. When the microphone of the hearing aid is off, it will actually eliminate all background noise and allow the user to concentrate on the phone call without distraction. With that said, it should be noted that people with a more severe hearing loss might find it difficult to hear his or her own voice while speaking. Most hearing aids will allow the option of turning the microphone on (at incremental levels) along with engaging the T-coil, to alleviate this issue. Consult with your hearing instrument specialist to determine which settings would be the best for you.
- The phone needs to be held near the T-coil and not strictly over the ear. With so many behind-the-ear (BTE) hearing aids currently being dispensed, it should be noted that the T-coil is in the hearing aid and not in the ear mold. In this case of a BTE hearing aid, the user should position the receiver of the phone above the ear in close proximity of the actual hearing aid. Practice moving the phone receiver around until the signal is the strongest. Although this positioning of the receiver may seem awkward at first, the benefits should be quickly realized.
- As a rule, most receiver-in-canal (RIC) and all completely-in-canal (CIC) hearing aids do not have a T-coil. Due to the size limitation of the hearing aid, the RIC hearing aid manufacturers (with some exceptions) have opted to forego the T-coil in favor of a smaller hearing aid. Please check your user’s manual or consult with your hearing specialist if you have any questions about whether or not you hearing aids are equipped with a T-coil.
- T-coils can also be used with loop systems. A loop system also creates an electromagnetic field similar to the coils previously discussed. These loops can vary in size from a personal neck loop to an encircling an entire room. This system can be attached to various audio devices such as a television, stereo equipment, or public address system. The user gains the same benefits using a loop system as he or she would when using a telephone including the elimination of background noise and clear processing of the incoming signal from the device which is attached to the system.
For a number of years a select few manufacturers have been working to transition high frequency sounds into a lower range where the user can hear better. Some people who suffer from a hearing loss can actually be completely tone deaf in some of the high frequencies ranges where consonants are heard (i.e. “f”, “s”, and “th”). This tone deafness results in the perpetual “mumbling” that cannot be overcome with even the most powerful hearing aids. Recently this has been changing in dramatic ways. Through various methods (depending on the manufacturer) these higher pitched sounds have been compressed to the lower frequencies which are in the auditory range for many users. This adds a whole new set of sounds that gives the user a new ability to hear what might have been missed before, and also the differentiation between these sounds to identify them to give a new ability to understand speech which may have normally sounded the same. If you have ever been told that there is nothing that could be done to get the high pitch sounds back, it is time for you to inquire about this new technology.
Some of the most recent technology changes in the industry are how hearing aids are now connecting with other electronic devices. Now virtually any device which will output an audio signal can be connected with a compatible hearing aid. A commonly used method is through Bluetooth technology. This allows a user to use a wireless connection to some of his or her favorite devices such as a cell phone, television, computer, stereo, or personal media device. Some of my patients have even connected to GPS systems and stethoscopes! The potential possibilities are limited only by the imagination of the user. While this technology may seem a little intimidating to some, I suggest keeping an open mind to this option. Although it is a very complex technology, it is generally very simple operate, and can open up a whole new world of listening enjoyment for the hearing impaired.