19th February 2015
Hearing Aid Features, What Are They & How Do They Help?
So what are the hearing aid features that matter?
Most digital hearing aids have a series of different features that are designed to deliver different benefits to the people who use them. All modern hearing aids from every manufacturer will have some mixture of features, however the feature set is dependent on the level of technology of the hearing aid and the manufacturer. The best or highest technology hearing aids from each manufacturer tend to have the best feature set available. These features are really algorithms or mini programmes that run on the processor brain of the hearing aids.
Exotic Names From Different Manufacturers
The features quite often have exotic names given them by their manufacturers. No two names are usually alike, however the underlying concept of the features are usually the same. That doesn't mean that the features work in the same manner or are as good as each other. Each manufacturer is esteemed for different things and that usually changes over time.
For instance, Starkey and Phonak are accepted as having the best feedback cancellation systems in the business. Widex is accepted as having the only noise reduction system in the business that actually assists the understanding of speech. Over time these things will change and those venerable manufacturers will become revered for something else.
An audible indicator is designed to inform you of changes in the hearing aid function. For instance when you change programmes in the hearing aids, you will hear a series of beeps, one for programme one, two for programme two and so on. When you turn the volume control up or down, you will hear a series of beeps that either get louder or softer. Usually when the battery is running low you will hear a series of two beeps the continue consecutively.
Widex, a Danish manufacturer mentioned earlier, actually use real recorded speech for their indicators. They will announce to you the programme that you are on and whether your battery is running low. Widex have even made this feature available in many world languages. They are one of the very few manufacturers to use this feature and it is available across their range of hearing aids no matter what the technology level.
Listening programmes are a series of pre-set parameters in hearing aids that are laid out to give the most benefit in differing listening situations. This ensures that the hearing aids are optimised for different listening conditions. Each listening program can then be selected by the user using a switch or push button on the hearing instrument or via a remote control. The general listening conditions that are usually set are speech, speech in noise, music and acoustic telephone.
Automatic programmes are simply a function that selects the optimum instrument settings without the user having to interact with the hearing aids in any way. The hearing instruments analyse and identify the current listening environment. Depending on what the aid thinks it is, it will then switch the parameters within the hearing aids to the appropriate settings. Differing manufacturers provide automatic programmes that recognise differing amounts of environments.
Binaural synchronisation is a very useful feature that was introduced several years ago. The feature ensure that the current user settings are synchronised across the two hearing aids. Put simply if you make a change on one hearing aid, this feature ensures that the second aid changes in the same manner. This means that the two hearing aid devices are always in the same programme and at the same volume level.
This is a feature that has been more recently introduced, Widex introduced it in their top range Clear hearing aids in 2009. Many of the manufacturers have followed suit in more recent times introducing the feature under differing names. Binaural compression allows hearing aids to work as a combined system to produce sound as naturally as possible. The feature only became possible when hearing aids begun to use in depth wireless communication.
Binaural compression is achieved by using both hearing aids to analyse the surrounding sound environment. They gather this information and then compare their versions of it. This information is then used by the hearing aids in a combined manner. This information allows hearing aids to work as a system for the very first time. Allowing them to make decisions on sound output as a system.
Using natural sound cues such as temporal effects (time differences in sound) and the head shadow effect (differences in sound from one ear to the other) to assess exactly what is going on in the sound environment and where the sounds are coming from. They then replicate these sound cues in their output, which allows them to deliver the most natural sound experience.
The feature undertakes all of these calculations and communications instantaneously, ensuring that there is no time lag on the output of the sound to the user. Because the natural sound cues are preserved, it is easier for the brain to do what it does naturally and the sound is perceived as a more natural sound.
Channels and bands, each manufacturer uses the terminology differently which can be irritating. However they are just ways to explain a division of something. In this case it is a division of compression. Compression, is what allows us to make a sound loud enough for it to be audible for you.
The division of compression into channels allows us to apply different levels of amplification to different sounds. In this way, we can make soft sounds audible but control loud sounds so they are not uncomfortable.
Compression channels are divided in a similar fashion to frequency bands which we will talk about later. This division of channels allows frequency-specific adjustments to be made independently in each area. Some hearing aids have more channels/bands than others.
Data logging is a feature that is available within most hearing instruments, the feature records different information during the hearing aid’s use. These sets of information are then made available through an interface to be analysed by the hearing professional.
The information can be very useful to assist a hearing professional during the fine-tuning of the aid. The data recorded usually includes the hours of use, the types of sound environments encountered, the listening programmes used and the volume control position and changes during that period.
Based on that information we can customise the hearing aid better to reflect your day to day requirements.
Feedback is one of the things that was once most associated with older hearing aids, it is the whistle that hearing aids sometimes emit. There are many reasons that hearing aids can feedback, feedback can be due to a poor fitting of an ear mould or in ear hearing aid, which allows the amplified sound to escape. That causes a feedback loop exactly like the squeal you hear at an event if someone with a microphone goes to close to a speaker.
In the case of a bad fitting, a new impression can be taken and the hearing aid or ear mould can be re-made to deliver a tighter fitting. Earwax can often be a cause of hearing aid feedback. If the ear wax becomes excessive or impacted within the ear canal, this will cause feedback. Another cause of feedback is close proximity to something, for instance if you place anything over your ear, a hand or hat or a person hugging you, that can cause feedback as well.
Feedback cancellation features differ in their operation from manufacturer to manufacturer and technology level. Some use phase cancellation, some use gain cuts, most also use a combination of both. Each type of system identifies the feedback and which frequency or frequencies it is occurring in. It then takes the feedback frequencies and either reverses the phase of the feedback signal and combines this with the original, resulting in the feedback being cancelled, or cuts the gain in the frequency to eliminate the whistle.
The problem with a gain cut is that the frequency may be important for speech, so cutting the gain is counter intuitive. Most manufacturers would use phase cancellation until it can no longer do the job and then kick in gain cuts.
Adaptive feedback cancellation
This feature is exactly the same as the feedback cancellation feature, but it is able to automatically adapt its speed of operation to improve performance under different environments, for example use of telephone, music and alarm beeps. When you are listening to music you actually want the feedback canceler to be less aggressive because musical notes can sound or appear to be feedback.
Directional microphones are the feature that has the single biggest impact on a hearing aid user's ability to hear in noise. A hearing aid with a directional microphone feature uses the information supplied by two microphones, to allow the processor to separate what sound is coming from the rear and what sound is coming from the front.
This allows the processor to reduce the level of sound coming from the rear and concentrate the sound coming from the front. Directional microphones enable you to change the direction of of the focus, as you require, from hearing all-round sound to being more focused on a single person or object to the front.
Adaptive directional microphones
This feature continuously adapts the focus of the microphones to detect the location of the strongest noise source and adapt the sound to minimise that noise. If the noise source moves then the null from the microphone system adapts to keep that noise source reduced.
Most adaptive systems can work in more than one frequency band allowing the reduction of several different noises simultaneously even if they are all moving at different positions once they are at differing frequencies.
Automatic directional microphones
Automatic directional microphones select their mode of operation according to the listening environment. In a quiet situation they will operate in an omni-directional mode (taking in sound from all around) and adaptive directional mode if available when a noise source is introduced.
The sound we hear is split into frequencies, early in life we can hear up to 20Khz, but by the time we are in our late teens that has fallen to about 12 or 14Khz. In order to process sound effectively the bandwidth or total frequency range of a hearing instrument is divided into a number of bands in which the amplifier gain can be controlled to match your hearing loss.
The amount of frequency bands and the frequency band width of hearing aids can be very different. By that I mean the amount of bands that sound is split into and the frequencies that a hearing aid can process and the complete . Some hearing aids can only accept and process sound frequencies from 200 hz to 6 Khz, others can accept and process from 100 hz to 11.5 Khz. The most important cues in human speech is normally between 200 hz and 4 to 6 Khz, however for the full and rich enjoyment of music, a much wider bandwidth is more desirable.
If you can imagine the old graphic equaliser features on a music system, frequency bands in hearing aids are used in a similar manner. Again each manufacturer is different, some hearing aid manufacturers call them bands and some call them channels. The feature allows the hearing professional to tune the hearing aid to a more customised range of sounds that you need to hear more clearly.
The more frequency bands that the aid has, the finer the tuning can be to match those ranges of sounds that you need to help with your hearing. So you end up with crisper, clearer hearing. Not just that, the more bands there is in the instrument the more bands that all of the features in the hearing aid can work independently. There is quite a bit of debate about how many bands matter, the opinion differs among manufacturers. For instance Widex, believes that fifteen is the limit, that any more than fifteen brings no more benefit, however GN ReSound believe that 17 is the best. No matter, the more bands or channels that a hearing aid has the better it is for you as a user.
Noise reduction is also discussed as a feature that makes speech clearer in noise, for the most part it actually doesn't. What it actually does is make noisy situations more comfortable. Only one manufacturer, Widex, have ever produced a noise reduction feature that actually affects makes speech clearer in noise,
The feature has been proven, in laboratory conditions, to affect signal to noise ratio. Signal to noise ratio is a key indicator of expected speech understanding. Most noise reduction features reduce the amplification of non-speech sounds in an effort to allow better understanding of speech sounds. In reality it makes it more comfortable in noisy conditions by automatically sensing and then reducing the background noise, for example in traffic noise in the street, busy pub or restaurant.
Speech enhancement is used with traditional noise reduction, speech has different sound patterns to background noise. Speech has certain parameters while background noise has different parameters or characteristics. Speech enhancement allows the processor in the hearing aid to identify speech signals and amplify them. In essence it analyses sound signals and, where most noisy, reduces background noise and maximises the speech signal.
Transient noise reduction
This feature is a noise reduction system that identifies and suppresses annoying impact sounds, such as breaking glass, shutting doors and clanging dishes, without affecting speech clarity. It is known by many names such as sound-smoothing, hammer noise protection and anti-shock depending on the hearing aid manufacturer. The feature allows the hearing aid to process sudden loud noises in a more comfortable way for the listener
Wind noise reduction
Wind noise reduction is an electronic system that reduces the annoying sound of wind cavitation on the microphones. The hearing aid detects windy conditions and adapts the hearing aid sound output automatically for maximum comfort.
This feature is particularly useful for people who participate in outdoor activities, such as golf. Some manufacturers use a design feature in their hearing aids to reduce the cavitation, in other words the design of the microphone cover is such that it physically reduces cavitation.
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