Understanding in noise is one of the biggest complaints of individuals with hearing loss who don’t wear hearing aids. Unfortunately, many hearing aid users have similar complaints and don’t report much improvement while wearing their hearing aids in noisy situations.

There is a simple explanation for why some hearing aids don’t provide much benefit in noise and it is based on the signal-to-noise ratio. The signal-to-noise ratio is a number that defines the level of the signal relative to the level of the noise for a given situation. In any listening situation, the signal is what I want to hear, and the noise is anything else that happens to be audible at that time. For example, if my wife asks a question like: “Will you take out the trash,” while the television and dishwasher are on, I have difficulty understanding what she is saying. Her voice is the signal and the TV and the dishwasher are the noise. The signal-to-noise ratio is the level of my wife’s voice minus the level of the TV and dishwasher. If the levels of the signal and the noise are the same, then the signal-to-noise ratio is 0. OK, I said all that to get this: The only way to improve understanding in background noise is to improve the signal-to-noise ratio! So, in my example above I improve the signal-to-noise ratio by muting the TV and turning off the dishwasher, easy enough right? What if we are in a situation like a restaurant or meeting, where I have less control over the environment? It is not as easy to simply turn down the noise.

Hearing research tells us that people with hearing loss need a better signal-to-noise ratio than people with normal hearing to understand speech. So, how do hearing aids affect the signal-to-noise ratio? The answer is many hearing aids don’t change the signal-to-noise ratio for commonly encountered noises. In a hearing aid with a single microphone, speech and noise are mixed as they enter hearing aid. As the hearing aid amplifies the sounds and delivers them to the listener, the speech and noise remain mixed. While the sound coming out of the hearing aid is usually louder than what came in, there is no difference in the signal-to-noise ratio. Remember, we said that the only way to improve understanding in noise was to improve the signal-to-noise ratio, so many hearing aids do not significantly improve understanding in noise. Sounds pretty sad huh? Well, there is hope for people with hearing loss roaming around in noisy situations and it’s called the directional hearing aid.

There has been much focus in recent hearing aid research on directional hearing aids. While on faculty at Vanderbilt University, along with several colleagues, I conducted studies that demonstrated that hearing aids with directional microphone technology can significantly improve the signal-to-noise ratio and thus make improvements in speech understanding in noise. Similar findings have been published from a number of pretigious research labs. Directional microphone hearing aids are more sensitive to sounds arriving from the front of the listener than those sounds coming from other locations. So by positioning oneself with the signal in front and most of the noise behind it becomes easier to understand in noisy environments!

Directional microphones can be incorporated in many different styles and technologies of hearing aids. While the most basic directional hearing aids remain in directional mode all of the time, more advanced digital hearing aids offer the listener options for listening in noise and in quiet. Today's most advanced hearing aids can automatically detect the need for directional microphones and turn them on and off depending on the amount of noise in the environment. Additionally, adaptive directional microphones can selectively change the sensitivity of the hearing aids depending on the direction that background noise is coming from.

Advances in hearing aid technology have improved our ability to help listeners with hearing loss understand in background noise. By improving the signal-to-noise ratio, we can provide better performance in noisy environments. With technology continuing to improve, individuals who wear hearing aids now have better noise-reduction options in personal hearing aids. So the not-so-unique of story of having trouble in background noise does have a viable solution. While we have not solved all of the problems associated with hearing aid use in background noise, advances in hearing aids are offering new opportunities to improve understanding for individuals with hearing loss. Meanwhile, I’m running out of excuses for not hearing my wife tell me to take out the trash!