9th February 2015
Hearing Aid Features, What You Need To Know and The Benefit You Can Expect
Modern digital hearing aids have a plethora of different features that are designed to deliver differing benefits to hearing aid users. All modern hearing aids will have some mixture or level of features, the feature set is often dependent on the level of technology of the hearing aid and the manufacturer. The best or highest technology hearing aids from each manufacturer have the best feature set available. Whilst we speak about features, they are usually not physical features but algorithms or mini programmes that run on the processor.
Hearing Aid Audible indicators
An audible indicator informs you of changing parameters in the hearing aids, for instance, which programme is currently in operation, that the volume control has changed or that your battery is running low. In most hearing aids these tones are usually a beep, however, Widex employ real speech to announce the programme that you are on and whether your battery is low. Widex has 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.
Automatic programmes
Before we talk about automatic programmes, first of all we need to talk about listening programmes, listening programmes are a number of pre-set listening situations that are programmed into hearing aids. This allows the hearing aids to have its settings 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 listening conditions are usually set as speech, speech in noise, music and acoustic telephone.
Automatic programmes select the optimum instrument settings without the user having to push a button or use a switch. The hearing instruments analyse and identify, the current listening environment automatically, it then switches the parameters within the hearing aids to the appropriate settings. Differing manufacturers provide automatic programmes that recognise differing amounts of environments.
Binaural synchronisation
Binaural synchronisation is a useful feature that was introduced several years ago. The feature ensures that the current user settings are synchronised across the two hearing aids. This feature ensures that if you make a change on one hearing aid, such as the changing the listening programme or volume control setting. It is automatically changed on the other to reflect this. This means that the two devices are always in the same programme and at the same volume level.
Binaural Compression
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. Binaural compression is achieved by using both hearing aids to assess the surrounding sound environment. This information is then used by the hearing aids in a combined manner. This mass of information allows the hearing aids to make decisions on sound output as a pair or 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. They then replicate these sound cues which allow 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.
Compression channels
Compression channels are divided in a similar fashion to frequency bands which we will talk about later. However, unlike frequency channels that are designed to change how frequencies are amplified. Compression channels are divided into a number of channels that restricts or changes the level of amplification within one sound frequency. The feature can be used to programme the hearing aid to amplify or reduce the range of noises that you hear. 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
Data logging is a feature that is available on most hearing instruments which records different information during the hearing aid’s use. These sets of information are then available to be analysed by the hearing professional to assist in fine-tuning of the aid. The data recorded can include 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 the hearing professional can programme the hearing aid to your specific requirements. This data logging is also used by some hearing aids to automatically change how the hearing aid works based on your preference over time.
Feedback cancellation
Feedback is one of the things 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 amplified sound to escape. In the case of a bad fitting, a repeat impression may be taken in order that the hearing aid or ear mould can be re-made to deliver a tighter fitting. Earwax can also 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
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 hearing, 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 is a feature within the processor which uses 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.
Frequency bands
The total frequency range of the hearing instrument is divided into a number of bands in which the amplifier gain can be controlled to match your hearing loss. It is also of interest to note that the frequency band width of hearing aids can be very different. By that I mean the amount of sound frequencies that a hearing aid can process. 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. 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 across. 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.
Noise reduction
Noise reduction is also discussed as a feature that makes speech clearer in noise, for the most part it actually doesn't. Only one manufacturer, Widex, have ever produced a noise reduction feature that actually affects signal to noise ratio (snr is used to measure the ratio of signal, speech, to noise). 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
Speech enhancement is used in combination with traditional noise reduction, speech has different sound patterns to background noise. On an spectrogram, 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 enhance or 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 hearing aid manufacturer. No matter what it is called, it allows the hearing aid to process sudden or 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.
