Hearing Aid Features
Hearing aid technology has improved leaps and bounds in recently years, especially with the introduction of digital hearing aids and computers. We have compiled the most common hearing aid features available. These features may or may not be beneficial to you depending on your hearing loss severity and your environment. Do not automatically pay for the "best" unless you do not have to worry about money. A hearing aid can easily cost you over $6,000.
Wide Dynamic Range Compression
With wide dynamic range compression (automatic gain control), the hearing aid circuit will automatically amplify softer sound more than louder sounds. This eliminates the need of fiddling the volume control and offers some protection from loud noises. Experiments have shown that this feature is more beneficial to people with severe hearing loss; however "automatic finger control" can achieve similar results.
Some hearing aids even eliminate the volume control totally; however many people still prefer to have the volume control available in additional to the automatic gain control.
Feedback Suppression is a mechanism for minimizing the effect of output signals from the hearing aid from interfering with the input resulting in loud annoying and screeching sound. This can happen when the output sound is picked up by the microphone or the vibration from the speaker reaches the input microphone via the casing.
Direct Audio Input
Direct Audio Input (DAI) allows the hearing aid to be directly connected to an external audio source like a CD player, TV, or an assistive listening device (ALD). By its very nature, DAI is susceptible to far less interference, and yields a better quality audio signal. It is an important option for people who need to use the telephone around sources of EMI such as computer monitors or heavy machinery. DAI capability is usually available only in selected behind-the-ear hearing aids. Wires connecting the hearing aid to a device need to be well-shielded as they can unintentionally act as antennas for nearby radio transmitters.
Many owners of BTE hearing aids don't realize that the hearing aid has DAI capability. Look at your owner's manual or hearing aid to see if there are metal contact points on the hearing aid.
Telecoils (T-coils, T-switches)
A telecoil is a very small coil of wire inside a hearing aid that serves as an antenna, which can pick up electromagnetic signals generated by hearing-aid compatible devices, such as telephone, special purpose microphone, and induction loops. The signal is then converted to sound by the hearing aid. The telecoil can be activated by the switch on the hearing aid when it is set in the "T" position. Using telecoil avoids the feedback that often results from putting a hearing aid up against a sound source, helps over-amplification and eliminates background noises. Telecoil provides much better access to the source.
Telecoils can pick up electromagnetic interference from certain computer monitors, heavy machinery, airplanes and digital mobile phones. Sound through telecoils may sound different than through the normal mode of the hearing aid. T-coils are often ineffectively positioned in canal and in-the-ear hearing aids due to the lack of room inside the hearing aid for optimal placement. The need to turn the telecoil on and off can be troublesome for new users, elderly people, and other people with cognitive disabilities.
During a normal face-to-face conversation, voice is normally coming from one direction with noise from all directions. The voice may be masked by noise, which makes comprehension difficult. In hearing aids with directional microphones, they can pick up sound from a specific direction only and tune out other noises. An improvement of over 3dB in signal-to-noise ratio is possible.
There are 4 types of directional microphones - manual fixed, automatic fixed, manual adaptive, and automatic adaptive. Fixed and adaptive refer to the microphone's directionality or polar pattern, which indicates how sensitive the microphone is to sound from different directions. Adaptive directional microphones can change the polar patterns as needed. Manual and automatic refer whether the polar pattern change is performed manually or automatically. See Directional Microphones for more details.
Even the electronic circuitry may be fixed, its performance can be programmed via a computer or by some controls. The control circuitry can also operate automatically. This type of programmable circuitry is generally more flexible than simple adjustable controls. Both analog and digital hearing aids can be programmable.
Some hearing aids have memory to store several profiles and they can be activated either by remote controls or switches. Each profile can be catered to a particular environment, such as noisy background, listening to TV or music and phone conversation.
For young children, multiple memories are useful when hearing loss is progressive or fluctuates over time. This feature would allow changes in hearing aid response to be available quickly. In some cases, having multiple settings readily available, parents can help their child to determine which setting provides the best audibility. With young children, parents should take charge of the program settings and make changes as needed.
Digital Hearing Aids
Digital hearing aid converts incoming sound to digital signals, which allows different types of signal processing and programs to be applied. The flexibility far exceeds what can be provided by an analog hearing aid. In general, it provides clearer sound, multi-channel processing, better noise filtering, and more complex tone control. Changes can be made simply by changing the program, which extends the usability of the hearing aid.
FM and Infrared Systems
They are similar to telecoils except that FM or infrared is used to transmit the audio signals.
FM systems have been used in educational settings to overcome the problems of listening in noisy classrooms. The teacher wears a small microphone and transmitter and the child wears a hearing aid and receiver. Sound is sent directly to the child via wireless FM transmission. These systems have been shown to improve communication in difficult situations. Many pediatric audiologists now recommend these systems for use in non-educational settings as well. They are most commonly used in any situation where high background noise, echoes or distance can make listening and understanding difficult. Some examples are watching television, car trips, family outings, field trips, and religious services.