Winning the War Against Hearing Loss, Part 5: Frequency Compression and Dead Zones

Bob Martin
July 28, 2015

The 10 articles in this continuing series entitled “Winning the War Against Hearing Loss” discuss miracles of modern audiology. So far, I have discussed Kim, whose hearing aids enabled her to go back to work in the high-level noise of a bar, and David, a real estate broker, who has overcome his problems using a cell phone with his hearing aids.

Today, our focus is on Dr. Judy, a school psychologist. When she first came to our office as a patient, she told me, “I don’t hear well at work. I have great difficulty understanding the kids. My job has become very difficult.”

Dr. Judy has precipitous hearing loss in both ears. Her audiogram falls to complete deafness in the higher frequencies, which are “dead zones” for her. She had worn hearing aids for years when I met her, but even with them her word understanding ability was inadequate. She wondered if new hearing aids could improve that.

I told Dr. Judy that new hearing aids could help her, but, I warned, the type of hearing aid fitting that she would need is difficult to get used to. She agreed to give it a good trial. I fitted her with RIC (receiver-in-the-canal) hearing aids and occluding earmolds.

Overview of the Fitting

Dr. Judy’s old hearing aids had large vents that allowed the amplified sound in the low frequencies to escape. The earmolds for the new hearing aids have small vents. Decreasing vent size causes her own voice to sound unnatural to her, which is a negative. However, the smaller vent size allows us to extend amplification down to 100 Hz. Very-low-frequency amplification can be very helpful for people like Dr. Judy.

Consider this problem from a “speech production” point of view. Dr. Judy was unable to hear high-frequency sounds like the “s” sound in the word “soup.” And, while she may still not hear the “s” sound with her new hearing aids, if they provide her with all of the rhythm-and-intonation cues in human speech, her ability to make speech sounds (i.e., her ability to talk) will help her guess the sound that she cannot hear. That is because the rhythm-and-intonation cues tell her the movements of the tongue, soft palate, and lips, so her ability to guess the sound correctly improves as she uses the new system. Adding sound in the very low frequencies is the first part of this fitting.

These new hearing aids also use frequency compression, which moves “speech information” from the higher frequencies, where Dr. Judy can’t hear sound, down to a lower frequency zone, where she has functional hearing. Sounds that were inaudible become audible.

So, how does she use wide-band amplification at work?

The fitting has two programs. Program one is a wide-band response that markedly improves her hearing in very-low-frequency zone. Also in this program, information from the high frequencies is moved into her audible range. Dr. Judy uses this program much of the time.

On days when the noise level in her office at school is high, she uses Program two to remove unwanted background noise. She activates the program and adjusts the volume to hear the student. Extraneous sounds are reduced markedly.

When asked about her new hearing aids, Dr. Judy says, “Oh, they are a lot better! I no longer have to struggle to hear the kids.”

Technical note: This is not a simple, easy-to-do fitting. It takes an advanced skill level to program this fitting. Also, a cooperative, highly motivated patient is a must.

Today, Dr. Judy is a happy working professional. The kids love her, and they and their parents are delighted that she is able to continue doing her important work as a school psychologist.

Next time, we’ll talk about Sam. See you then.

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