In my last couple of blog posts I discussed the use of “listening programs” to improve hearing. Today I want to continue this discussion and cover the difficult topic of “How to enhance word understanding and simultaneously reduce background noise.”
When I tackle this problem, hearing when it is noisy, I first ask myself, is it possible for this patient to hear when the background noise level is high?
Shown below are the hearing thresholds for two patients, Sharon, the schoolteacher whom I wrote about in my last post, and Joe. Their hearing is the same in both ears, so only one set of pure-tone thresholds is shown.
Sharon has a moderate hearing loss bilaterally. Her pure-tone thresholds are:
40 dB at 250 Hz, 50 dB at 500 Hz, 60 dB at 1000 Hz, 60 dB at 2000 Hz, 60 dB at 4000 Hz, and 65 dB at 8000 Hz.
Joe has higher thresholds at all frequencies except 250 Hz. hearing loss bilaterally. His pure-tone thresholds are:
30 dB at 250 Hz, 55 dB at 500 Hz, 65 dB at 1000 Hz, 75 dB at 2000 Hz, 90 dB at 4000 Hz, and no response at 8000 Hz.
Notice that Sharon and Joe’s hearing thresholds are roughly the same in the lower frequencies. However, Sharon hears significantly better in the higher frequencies. Compare Sharon’s thresholds at 2000 and 4000 Hz: 60 and 60 dB, to Joe’s 75 and 90.
If we use a cut-the-bass, amplify-the-high-frequencies strategy with both patients, the task will probably be much easier for Sharon than for Joe. A large reduction in low-frequency amplification will not leave Joe with very much hearing. Meanwhile, his hearing in the higher frequencies will still be poor.
In addition to studying a patient’s hearing, I also want to know the condition of their hearing aid microphones. If the hearing aids are more than a year or a year-and-a-half old, we will probably need to have them replaced before we work on a “noise-reduction” program.
This type of programming—reducing perceived noise—is one of the most important tasks that hearing aid professionals have to handle. The real world is noisy. Very noisy.
Fortunately, we have a multitude of professional tricks we can use to reduce noise: we can cut bass and amplify highs, activate a rear-facing microphone to cancel noise, or set AGC (automatic gain control) levels judiciously (making sure not to compress too much, which increases perceived noise).
WHEN ALL ELSE FAILS
When all else fails, my favorite trick is to match the hand-held-behind-the-ear frequency response (the REUR + hand) to the noise program. Most people hear well in high-level noise if they cup their hands behind their ears. And of course we need to eliminate all types of distortion and feedback from the amplified sound.
Finally, we have to place all amplified sound within the patient’s acceptable audibility range. Other than that it is easy–just joking :-).
See you next time, when we will continue this discussion.