What are hearing aid channels?
When you first hear about hearing aid channels, you may understandably think that the term refers to programs, given that when you change television channels, you are changing programs. However, hearing aid channels are not to be confused with hearing aid programs or volume control which are manual settings that can usually be adjusted by the hearing aid user, if activated. Hearing aid channels have to do with the way sound is processed by the hearing aid. They are processing channels available for programming and cannot be adjusted by the wearer. To understand hearing aid channels, it is important to understand that sound comprises different frequencies (pitch), and that hearing aids process and amplify sound based on frequencies and volumes.
When your hearing is tested, your thresholds (the softest sounds you can hear) at different frequencies are determined. A threshold is the lowest intensity (volume) level needed to hear a frequency, in other words where it is just detectable or audible. If you were shown your audiogram after your hearing test, you may have noticed the different frequencies indicated as well as your thresholds at those frequencies. Usually, the frequencies of 125Hz – 8000Hz are tested. Much like a piano keyboard, the lower frequencies (bass sounds) are depicted on the left of the audiogram, and the higher frequencies (treble sounds) on the right. You may be able to hear certain frequencies better than others, and if you have a hearing loss there may be certain frequencies that are more affected than others. You may therefore require different amounts of amplification at different frequencies.
Hearing aid channels are groups of frequencies or frequency areas. Another way of defining a hearing aid channel is a range of frequencies that is created by a digital filter or series of digital filters within the hearing aid. Hearing aid channels break down the frequency spectrum into areas (frequency ranges) for signal (sound) processing.
Hearing aids handle all frequencies in a particular channel (or group) together, as one entity. Therefore, frequencies in a particular channel are analyzed, processed, and reproduced in the same way. For instance, a single-channel hearing aid handles all incoming sounds as one sound. In this case, the average level of sound is analyzed, processed with the same gain (amplification) applied to all frequencies, and the amplified sound, although louder, is delivered with its original characteristics.
On the other hand, a 3-channel hearing aid might handle all sounds under 1000Hz as a low-frequency channel, all sounds from 1000Hz to 3000Hz as the mid-frequency channel, and sounds above 3000Hz as the high-frequency channel. The hearing aid would then analyze the average level of sound in each frequency region (i.e. low, mid, and high). If necessary, a different amount of gain (amplification) could be applied to each channel (frequency region) if required, based on the hearing loss.
A multi-channel hearing aid (a hearing aid with more than one channel) does not cover more frequencies, but the incoming sound is divided into more than one frequency region to be analyzed, processed, and reproduced separately.
So, when we talk about hearing aid channels, we are referring to how frequencies are distributed for processing, and when we talk about the number of channels, we are referring to the number of channels available for programming.
Why do hearing aids have channels?
Hearing aids use channels for better sound processing. One of the main benefits of breaking up the frequency range into channels is that it enables hearing aids to differentiate between speech and noise. Different amounts of gain (amplification) can be applied to each channel. This is important because you do not necessarily want the same amount of amplification at all frequencies. Usually, noise is more of a low-frequency type sound, while speech is more of a high-frequency sound. If a hearing aid only had one channel for instance, the same amount of amplification would be applied to all frequencies in that one channel.
However, the benefits of multiple channels extend beyond the amount of amplification. Hearing aids can also apply different features to varying degrees in different channels. In fact, the operation of most signal processing features (e.g. expansion, compression, noise reduction, feedback cancellation, and multi-channel directionality) is channel-specific. So, if a hearing aid only had one channel, the same features would also be applied to all frequencies in that one channel. Hearing aid channels contribute towards more specific processing and amplification of sounds received by a hearing aid.
What are the benefits of having different channels?
One could say that the more channels a hearing aid has, the better the potential sound quality. This becomes increasingly apparent in difficult or challenging listening environments that require complex sound processing.
According to People Hearing Better, the advantages of multiple channels include:
- Improved speech vs noise differentiation: Hearing aids with more channels can identify more accurately which sounds are speech and which are noise. Unwanted noise can be suppressed by the hearing aid while enhancing sounds that are important.
- Improved environmental identification: Hearing aids with more channels can be programmed to sift through and recognize more sounds and identify the environment faster. Multi-channel digital hearing aids are able to change settings according to different environments, rendering a more natural and comfortable sound experience. The function of other hearing aid features can also be enhanced by a more accurate analysis of the sound environment.
- More precise identification of sound levels in more discrete frequency regions, resulting in improved sound environment identification for appropriate processing (e.g. noise reduction and compression).
- Improved fine-tuning or adjustments: The more channels a hearing aid has, the more scope the hearing healthcare professional has to fine-tune or adjust the hearing aids to better accommodate individual requirements and preferences. Having more channels effectively offers room for more personalization of hearing aid settings.
- Improved features: Sound quality can be improved considerably as a result of features and algorithms that are more advanced. For instance, a hearing aid with a directional microphone may function with more accuracy when there are more channels. If the hearing aid does not have a sufficient number of channels for the features to operate optimally, some features will not provide all the benefits that they have the potential to provide.
It is possible that increasing the number of processing channels may be beneficial for hearing aid signal processing techniques, and there are advantages of multiple channels for certain features. Examples of signal processing techniques and features that may benefit from multiple channels include:
- Noise reduction: Gain reduction can be isolated to the frequency region where noise occurs because the algorithm can more precisely identify which frequency region is speech and which is noise. Speech audibility can thus be preserved and listening comfort improved.
- Feedback suppression or cancellation: Gain reduction can be limited to a narrower range of frequencies, so the audibility of other frequencies is not affected.
- Directional microphones: In the case of the HD Locator, the adaptive microphone system can adjust for different frequencies, so that speech audibility in noise is preserved and improved.
- Target gain match: Compression settings and frequency response are capable of matching more hearing loss configurations, even those that are more unusual.
- Narrowband Automatic Output Control (AOC): Restricting limitation of output to a narrow frequency range, preserves other sounds’ audibility.
How many do you really need?
Contrary to what you might think, more channels are not always necessarily better. While multiple channels are desirable for analysis and processing of sounds, having them also poses certain risks, such as increasing the possibility of:
1. Spectral and temporal smearing
This is the reduction of the contrasts between the peaks and valleys in a speech signal. Such contrast is important for speech recognition, particularly for those with more severe hearing losses. There is potential with too many hearing aid channels, for the clarity of sound to be diluted or muddied. While the sound may be sufficiently loud, it may not be clear enough to hear the difference between similar sounds. Sounds can become ‘muddy’ when the number of channels exceeds 15 to 20.
Digital hearing aids process sound quickly. More channels pose the possibility that there may be a delay in sound processing. While this delay is normally only milliseconds, a difference of +- 5 to 6 milliseconds (msec) can be noticed by the average person. According to People Hearing Better, some multi-channel hearing aids’ change is up to 12 msec. They suggest asking your hearing healthcare professional about the delay for your multi-channel hearing aid or trying it out to see whether you notice a delay. Given the fact that many hearing aids are fit in an open-canal configuration, it is recommended that any delay not exceed 5 msec.
Hearing aid processors allocate time and power to certain functions. When there is an exorbitant number of channels, processing power may be diverted from other features or functions that may be important for issues such as the suppression of background noise.
Studies suggest that as little as 8 channels are sufficient to restore audibility, even in environments where background noise is present. While most people don’t really notice much of a difference in sound quality with more than 8 channels, this may not be your experience due to features and how your hearing healthcare professional has adjusted your hearing aid. Some people also have a more finely tuned ear. While one person may notice a significant difference between an 8 and 15 channel hearing aid, another may not notice any difference whatsoever.
Will you still be able to hear clearly with fewer channels?
Although the number of channels is undeniably an important consideration when it comes to deciding on a hearing aid, this is not to say that you will not be able to hear clearly with fewer channels. For some hearing losses, many channels may not offer a significant improvement compared to fewer channels. If you have a flat or mildly sloping hearing loss, having many channels may be superfluous for you. In fact, it appears that a three-channel hearing aid can restore frequency-specific audibility for these configurations.
In straightforward listening situations, even a basic hearing aid should provide adequate sound quality, but this may be compromised in difficult listening situations where there is background noise present. If you are looking for a hearing aid that operates well in challenging environments, you may wish to consider investing in a hearing aid with noise-canceling features and a sufficient amount of channels for these features to operate optimally.
Ask your hearing healthcare provider to make a recommendation that is best for your particular hearing loss, listening needs, lifestyle, and budget. Ask as many questions as you would like to make sure you make an informed decision, including asking for a trial period before making your purchase.