HEARING AID TECHNOLOGY
Thanks to electronic technology, many features are available for hearing devices. Overall, the more sophisticated the hearing aids, the better user performance and therefore satisfaction. The cost will reflect the level of technology that the hearing aids incorporate.
Digital Hearing Aids
In digital hearing devices, sound waves entering the microphone are converted into digital format. They are then separated into different frequency bands and channels and converted back to analog format out into the ear canal as a sound wave. The hearing aid will adjust according to the sound environment the user is in. For example, the hearing aids process speech and recognize noise to enhance your listening environment. The sophistication of the algorithm used in the hearings aids varies between levels of technology. These devices are controlled and programmed by an audiologist with a computer.
Mid level Technology
Hearing Aid Features
There are many optional features that are available to order on hearing aids. Keep in mind that you do not need every feature! It is important to discuss with your audiologist what is right for you and your lifestyle. The lowest level of technology usually has the least amount of standard features, while the highest level of hearing aids have the most standard features. Some features to consider:
- Number of programs/memories
- Bands and channels
- Directional microphones
- Feedback management
- Easyphone, East FM
- Direct Audio Input
Hearing aids can have up to several programs, or "memories." Inside the hearing aids, the circuits work differently in order to maximize the benefit you receive in each listening situation. Different internal settings of hearing aids are optimal for different listening situations. There are many programs to choose from. Examples include: quiet, noise, music, cards, concerts, restaurants, etc.
Programs can be changed manually by the push of a button, or the hearing aids can adjust to your listening environment automatically. Hearing aids will alert you when a program is changed by signaling a number of beeps (corresponding to the number position spot of the program), or they may be able to use a verbal messaging system that will "speak" to you, indicating which program the hearing aids are operating in. The verbal messaging system may be set to a variety of languages.
The number of available programs depends on the manufacturer and level of hearing aids you choose to purchase. Every manufacturer has instruments in every level of sophistication.
Bands and Channels
A band refers to a frequency region where gain (loudness) adjustments are made. The amount of gain applied differs with each band, dependent on your hearing loss.
A channel refers to a frequency region where the same signal processing takes place. A channel incorporates a broader frequency region. It can be thought of as the background in signal processing.
The audiologist manipulates the bands to influence the algorithms and signal processing in the hearing aids. This allows for flexibility and fine tuning.
You can think of bands and channels in hearing aids as the keys and strings on a piano: the white keys represent the channels, and the black keys represent the bands.
The more channels hearing aids have, the more natural the sound quality will be to a patient; just as the more keys on a piano, the more increase in sound quality for the listener. Therefore, more bands and channels can help improve speech recognition. As the number of available bands and channels increases, so does the cost.
A conventional hearing aid microphone is also called an omnidirectional microphone. As long as there are no significant objects nearby to reflect or diffract a sound, an omnidirectional microphone will respond equally to the sounds from any direction. In other words, the microphone is equally sensitive to all incoming sounds, regardless of the direction of the sounds. No sounds are reduced in relation to others. Omnidirectional microphones are used best in quiet listening environments.
One of the best ways to improve speech recognition in a noisy environment is the use of a directional microphone (DM). In general, DMs are more sensitive to sounds from some directions than others. Traditionally, these microphones pick up and amplify sounds coming from the front of the wearer and attenuate the sounds from the side and behind the wearer. Therefore, DMs can help the wearer when listening in background noise.
A DM is the only hearing aid option that can improve your speech recognition in noise by improving the Signal to Noise Ratio (SNR). The SNR is the ratio of the desired signal's volume to the unwanted "noise," measured in decibels (dB). The ability to understand speech depends on how much of the signal can be heard in the background noise. People with a hearing loss require 5-15 dB better SNR than those with normal hearing to equally understand speech in noise. DMs can improve SNR by 4-5 dB.
As with all features, there are levels of technology within the design of directional microphones. As the technology increases, so does the price.
Feedback is a common problem with hearing aids that results in a whistling noise. It may be caused by the user's ear, the fit of the hearing aid to the ear, and/or the hearing aid itself. During the fitting process, a measurement is made of how much amplification can be given at each frequency without feedback occurring. This system ensures that the amplification can never be increased enough to cause whistling. Feedback managers range in their level of technology from simple single channel to advanced multichannel systems.
Hearing aids with noise reduction capabilities change their frequency gain characteristic as a result of analysis of the incoming signal (speech vs. noise). Various noise reduction strategies can be used to reduce ambient noise. Hearing aids work to determine a signal as noise and then reduce this signal. The use of noise reduction helps improve listening comfort in noise. Typically, manufacturers employ more than one noise reduction strategy for their hearing aids.
Sophisticated algorithms are used to estimate the nature of the signal and determine it as noise rather than speech. Each hearing aid manufacturer has a different approach to do this. Once it is determined that a signal is noise, gain adjustments across frequencies can be made. While the same basic premise is true of all hearing aids with noise reduction, there are levels of technology within this feature.
Noise reduction technology differs in hearing aids, depending on:
- The number of channels in the hearing aids
- The level at which noise reduction becomes active
- The maximum amount of gain adjustment made across frequencies
- Speed at which the filter changes its frequency response characteristics
So, the most advanced hearing aids have a noise reduction algorithm that is better at recognizing a signal as noise, acts quickly upon reducing the noise, and makes frequency-specific gain adjustments across multiple channels.
The degree of automatic operation that a hearing aid user chooses to have should be dependent on the amount of control they desire. It is possible to have your hearing aids do everything for you from the moment you turn them on. This includes adjusting the volume, changing programs, and changing modes (microphone, telecoil). If you want your hearing aids to be fully automatic or "hands-free", this indicates a high level of technology. Therefore, the hearing aids will be more expensive. Fully automatic hearing aids constantly monitor the listening environment you are in and make adjustments accordingly in order to provide maximum user benefit.
Telecoil and Easyphone/Easy FM
A telecoil is a small coil inside of a hearing aid that acts as a magnetic field sensor. The telecoil also senses any oscillating magnetic field (for FM system and other assistive listening devices).
When the hearing aids are in the telecoil mode (T), the microphone (M) is not being used. Therefore, environmental sounds are eliminated. In the telecoil mode, hearing aids only pick up sounds from the magnetic field that they sense, such as a telephone or FM system. Some hearing aids also have a microphone and telecoil (M+T) setting in order to receive acoustic and magnetic energy simultaneously.
Some hearing aids have a programmable telecoil. This means that the telecoil can be manipulated in terms of strength or loudness. It can be adjusted to provide the hearing aid user with a maximized signal. Telecoils can also be manual or automatic. A manual telecoil requires the user to change to the telecoil (T) mode by using a toggle switch on the hearing aid or with a remote control. An automatic telecoil will automatically switch from microphone to telecoil mode when near an electromagnetic source.
When using the telecoil, the common problem of feedback is eliminated.
Easyphone or Easy FM automatically recognizes when there is a magnetic field and adjusts accordingly, switching to the telecoil setting to pick up this type of energy. For example, when the hearing aid user picks up the receiver of a telephone, the hearing aids will switch into telecoil mode without having to press a button. The same can be done for use with an FM system or other assistive devices that use electromagnetic energy.
Direct Audio Input
This feature allows for direct connection to other devices such as assistive listening devices, televisions, computers, MP3 players, radios, etc. The signal is routed directly into the hearing aids from other devices. Assistive listening systems and other hearing assistive technologies can be of great benefit when either working separately from, or in combination with, your hearing aids.
Warranties vary in duration and therefore also vary in price. Considering how much hearing aids may cost, it is often worthwhile to have a longer warranty period, or extend it if possible. If you lose or damage your hearing aids when the warranty has expired, replacement and repair can be quite pricey.