Hearing loss results in two main problems; loss of audibility and loss of clarity in noise.
Loss of Audibility. This means that sounds are too soft to hear. We have a couple of strategies to make sounds more audible.
- Amplification. Today’s modern hearing aids selectively make softer sounds louder than louder sounds.
- Frequency Compression. In some hearing aids such as the ones provided by my company, Phonak, the hearing aid can shift high pitched sounds down to lower pitches. The logic is that you may have too much damage in the high pitches to amplify the sounds sufficiently, so we will shift these sounds to regions where you have better hearing.
- Cochlear Implants. If high powered hearing aids equipped with frequency compression no longer helps you hear, we now turn to a Cochlear Implant to make sound audible. See these links for more information of Cochlear Implants. Also here.
Loss of Clarity in Noise. I wish that hearing loss was merely a problem of loss of audibility. It would be so much easier just to amplify the sounds and be done with it. Just like wearing a pair of corrective lenses for vision, right? Wrong.
After we do our best to make sound audible, we also have to do something about getting rid of the background noise. As one’s hearing loss gets worse, not only do we need stronger and stronger hearing aids, but we also need to get rid of more and more noise. For example, a person with normal hearing can handle a signal-to-noise (SNR) ratio of 0 and still understand most of what is being said. An SNR of 0 means that the person talking to you is the same loudness as the person you don’t want to listen to. This happens all the time. Imagine a restaurant. There are people all around you talking at the same loudness as your significant other across from you. You normal hearing folks can handle this, people with hearing loss cannot.
Strategies to Hear Better in Noise.
- Ear Level Directional Microphone Technology
- Remote Bluetooth Microphones
- Fixed Gain FM/Infra-Red/Digital Technology
- Dynamic FM
These 4 strategies are not all the same. They vary significantly in the amount of noise reduction provided.
A directional microphone works by picking up the sound from one direction (typically the front) but not from anywhere else. So now you won’t hear the annoying kid in the restaurant behind you as much. Independent research has shown that a directional microphone on the hearing aid does help you hear better in noise compared to a regular omni directional microphone. The range of improvement found in these studies is anywhere from 3 to 8 dB. So it gets rid of about 5 dB of noise. This is not huge, but for people with milder losses of hearing, this may be all they need. It certainly is convenient. You don’t need to carry extra equipment. In fact, in today’s modern hearing aids such as Phonak Bolero Q or Virto Q, these microphones get switched on automatically when it gets noisy. Pretty awesome technology in there.
Remote Bluetooth Microphones.
Many companies, including the one I work for, now have affordable Bluetooth microphones that can be used with your hearing aids. You clip this microphone onto the person you want to hear and it transmits wireless via Bluetooth radio waves to a device around your neck which in turn sends it to your hearing aids. By moving a microphone from the ear level to a much closer proximity to the talker’s mouth, we can achieve much higher signal-to-noise ratios than a directional microphone located on your head. Here is the example from Phonak which involves the use of the Remote Microphone in conjunction with either a ComPilot or an iCom.
The advantage of Bluetooth microphones are that you get rid of more noise compared to ear level directional microphones. They are convenient, and easy to use with simple and intuitive controls (just an on/off switch and volume). Finally they have the advantage of low cost. It is a very affordable solution, much less than FM.
Traditional and Fixed Gain Wireless Systems
To achieve an improvement in SNR up from a Bluetooth Microphone system would be to use a fixed gain wireless system. Examples of include:
- Phonak’s 2nd Generation systems such as Campus, SmartLink SX, ZoomLink, EasyLink (silver casing)
- Oticon Amigo
- Comfort Audio Digisystem
These are all examples of fixed gain systems and achieve similar results. The reason these perform a bit better than the Bluetooth microphones is that most incorporate directional microphones on the transmitters and therefore can get rid of more noise. Additional benefits include greater operating ranges and longer battery life. However, cost is significantly higher for what is really just a modest improvement over a lower cost Bluetooth microphone system.
Adaptive Wireless Systems
Some wireless systems are adaptive. For example, the Dynamic FM technology that Phonak uses is different than fixed gain systems in that it adjusts the FM gain depending on the environmental noise level. Therefore additional gain is added if the background noise level increases. The technology works by measuring the ambient noise levels in the room during speech pauses. If the ambient noise level rises to over 57 dB SPL, a command is sent from the transmitter to the Dynamic FM receivers to increase the FM gain. When the FM gain increases, you get a higher signal to noise ratio. It is still comfortable to listen to because today’s modern hearing aids all have compression which keeps this at a comfortable level. Examples of Adaptive Wireless Systems include Phonak inspiro, SmartLink+, ZoomLink+, EasyLink+ and any 3rd generation Phonak receiver (eg MLxi, ML9i to ML16i)
How Do These Technologies Compare?
1. Directional Microphones vs Fixed Gain FM. This classic study by Valente et al in 2002 compares an omni mic to a directional mic on a hearing aid which in turn compares this to an FM system. The data is backwards, so the lower the number, the better the result. It is very powerful data showing how well an FM system can help over just an ear level directional microphone.
2. Fixed Gain vs Adaptive Gain Wireless Systems.
The most extensive study comparing fixed gain vs adaptive gain wireless systems was conducted by Dr. Linda Thibodeau, PhD, University of Texas at Dallas, USA, and the Callier Centre for Communication Disorders, Dallas. AFMA refers to the Adaptive Gain FM while Fixed of course refers to fixed gain wireless less. Remember that fixed gain wireless systems include Bluetooth microphones, Phonak’s second generation FM (Campus), Oticon Amigo, and Comfort Audio DigiSystem to name a few. As you can see, when the room noise gets louder, the word recognition score for the adaptive gain wireless system is much higher. In this example, the transmitter used was the Phonak inspiro with Dynamic FM.
3. Adaptive FM vs Digital Wireless.
This study, conducted at the University of Orebro in Sweden, compared a digital wireless system with fixed gain (Comfort Audio Digisystem) to a adaptive gain FM system (Phonak Dynamic FM). The question is what leads to better performance in noise. The result s clearly showed that the adaptive gain system (Phonak Dynamic FM) leads to better performance.
So which do you need?
I will make my next blog post on how to select the correct technology for your needs. But here are the summary points.
- You need technology that helps you not only hear soft sounds, but also helps get rid of background noise.
- Directional microphones on the hearing aid itself can get rid of about 5 dB of noise.
- Bluetooth microphones provide additional improvement in noise.
- Fixed gain wireless systems such Phonak’s second generation FM, Oticon Amigo and Comfort Audio Digisystem provide additional improvements over a Bluetooth microphone, but these may be modest improvements.
- Adaptive gain wireless systems such as Phonak Dynamic FM still provides the largest amount of noise reduction.