Digital Hearing Aids
The main difference between analogue, the conventional system, and digital, the new technology, is in their method of conversion. Analogue converts sound waves to electrical waves while digital converts sound waves using exact mathematical calculations that are processed by a computer.
Analogue Hearing Aids
- Do not distinguish different sounds and therefore amplify all sounds equally, which means some sounds, are too loud while others may be difficult to hear. This is rectified when the hearing aid user adjusts the volume
- Programmable analogue hearing aids are equipped with different programs that are saved in the aid. The programs are then switched depending on the listening environment. As an example, one program will work during a conversation, while the other may work best while in the theatre.
Digital Hearing Aids
- Translate sound to digital code, change it and re-transmit it back by using mathematical calculations.
- Duplicates sound transmission.
- Produces a high quality sound that is extremely accurate.
Many believe that the digital system has revolutionized hearing by accurately duplicating sound transmission. Digital hearing aids have many benefits and lots of automatic features, although some still believe that programmable analogue aids possess great sound quality and functionality and are great in that they are more affordable.
Can digital hearing aids help cut out background noise?
People who use traditional analogue hearing aids often complain that they find it difficult or impossible to follow conversations in noisy places.
Many digital aids are designed to reduce steady kinds of background noise, such as the rumble of traffic or the whirr of a fan. This can make listening more comfortable. But it does not necessarily help you to pick out a single voice from everything else going on, especially when several people are talking at once.
Two things have been shown to improve hearing in noisy situations more than anything else - wearing hearing aids in both ears, and using hearing aids that have directional microphones.
Directional microphone systems amplify sounds that come from in front of you more than sounds to the side or behind you. This makes it easier for you to focus on what you want to listen to in a noisy place. Most digital hearing aids have microphones that can be set to operate like this. This means you can switch between directional and all-round sound, depending on what you need to hear at the time. Some digital aids will detect where the noise is coming from and automatically adjust to reduce the noise selectively. However, a hearing aid cannot know what you want to listen to and so the reduction of unwanted sound can never be perfect.
Can digital hearing aids help reduce whistling?
Yes. Some digital hearing aids have feedback management systems. This means that they can automatically detect any feedback and try to reduce the whistling that bothers many people who use hearing aids.
More comfortable listening
Most digital hearing aids have some form of loudness compression system. This means the hearing aid can manage sounds of different volumes and only amplify them as much as you need. It means the aid can be programmed to suit your particular hearing loss and ensures that you always hear different sounds at levels that are comfortable for you. This type of aid is often completely self-adjusting.
It will only work well for you if the person who fits it also adjusts the settings carefully to suit you, when you first have it. You may need to have your aid fine-tuned again, when you get used to it.
- What is the 'T' setting?
It is usually possible to switch to the 'T' (telecoil) setting with a digital hearing aid, as it is with an analogue aid. The telecoil is a small component in the aid that picks up signals from a loop system or hearing aid compatible telephone. But your audiologist will need to programme the 'T' setting and show you how to switch over. If you choose a very small style of hearing aid that fits into your ear canal, there might not be room for a telecoil, so you won't have the 'T' option.
The Digital Advantage
Fortunately, for both dispensing audiologists and patients, there are features and advanced signal processing schemes available in current digital hearing aids that do have significant advantages over those found in analog instruments. Potential digital advantages include those related to:
- Gain Processing. One of the primary benefits associated with flexible gain-processing schemes is the potential for increased audibility of sounds of interest without discomfort resulting from high intensity sounds. While this is more generally a benefit of compression rather than digital processing per se, the greatly increased flexibility and control of compression processing provided by DSP--such as input signal-specific band dependence, greater numbers of channels, and kneepoints with lower compression thresholds--can lead to improved audibility with less clinician effort. Expansion, the opposite of compression, has also been introduced in digital hearing aids. This processing can lead to greater listener satisfaction by reducing the intensity of low-level environmental sounds and microphone noise that otherwise may have been annoying to the user.
- Digital Feedback Reduction (DFR). The most advanced feedback reduction schemes monitor for feedback while the listener is wearing the hearing aid. Moderate feedback is then reduced or eliminated through the use of a cancellation system or notch filtering. DFR can substantially benefit users who experience occasional feedback, such as that associated with jaw movement and close proximity to objects.
- Digital Noise Reduction (DNR). This processing is intended to reduce gain, either in the low frequencies or in specific bands, when steady-state signals (noise) are detected. Although research findings supporting the efficacy of DNR systems are mixed, they do indicate that the DNR can work to reduce annoyance and possibly improve speech recognition in the presence of non-fluctuating noise. DNR is sometimes advocated as complementary processing to directional microphones. While directional microphones can reduce the levels of background noise regardless of its temporal content, they are limited to reducing noise from behind or to the sides of the user.
- Digital Speech Enhancement (DSE). These systems act to increase the relative intensity of some segments of speech. Current DSE processing identifies and enhances speech based either on temporal, or more recently, spectral content. DSE in hearing aids is still relatively new, and its effectiveness is largely unknown.
- Directional Microphones and DSP. The ability of directional hearing aids to improve the effective signal-to-noise ratio provided to the listener is now well established. In some cases, however, combining DSP with directional microphones can act to further enhance this benefit. In some hearing aids, DSP is used to calibrate microphones, control the shape of the directional pattern, automatically switch between directional and omnidirectional modes, and through expansion, reduce additional circuit noise generated by directional microphones.
- Digital Hearing Aids as Signal Generators. Since digital hearing aids have a DSP at their heart, they are able to generate--as well as to process--sound. Current digital hearing aids use this capability to perform loudness growth and threshold testing in order to obtain fitting information specific to an individual patient's ears in combination with a specific hearing aid. Sound levels also can be verified through the hearing aid once it is fit. This technology has the potential both to increase accuracy of hearing aid fittings and potentially streamline the fitting process by reducing the need for some external equipment.
Current digital hearing aids are certainly exciting, and the future possibilities are endless. Before long, digital hearing aids will replace their analog counterparts altogether. We must, however, present this technology to patients in an informative and educational manner. Like many other high-tech devices, high expectations often accompany digital hearing aids. Counseling patients about appropriate expectations will continue to be more--not less--important as technology continues to advance.