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Miscellaneous: Audiometer, Digital Signal Processing, and Hearing Aids

A relative of mine has a hearing problem and today we and her mom went to see an audiologist for a free hearing check. The process began by the audiologist interviewing her about personal background, e.g. when the hearing problem started, whether she has ever had any accident, etc. We then proceed to the audiometer lab where she was asked to stay in an acoustically isolated sound booth for an audio responsiveness test.

My relative was asked to put on a headphone and the audiologist used an audiology workstation (a Pentium personal computer with hardware interfaces to audiology instrumentations, such as the audiometer). The workstation was used to generate the sounds of various frequencies and various loudnesses separatedly for the left ear and the right ear.

I remember the frequency range was logarithmically spaced from 250 Hz to 15,000 Hz, in various increments. For each frequency point, the audiologist started with a typical loudness, such as 60 dB, and increased/decreased the loudness up and down to get the minimum and maximum volumes that my relative can comfortably hear at particular frequencies.

The result of this audiometer test is an audiogram that looks like this one, which the responsiveness of the ears at particular frequencies. A verbal test to check for her linguistic problem was followed up. She passed the verbal test fine and was suggested to use the hearing aids to improve her hearing.

The audiologist then presented us a tiny pair of the hearing aids, described as of digital, behind-the-ear type. He wanted her to try them on and, to my wonder, he used a computer software to input my relative's audiogram and program it to the hearing aids by an instrument connected to the serial port of the computer.

From what he explained, advanced [Digital Signal Processing (DSP)] technologies was used in these digital hearing aids. The hearing aids are capable of monitoring sound inputs from the environment and adjusting the outputs to match the programmed audiogram data so that my relative can hear the world comfortably. The hearing aids are also smart enough to sense the unusually loud sounds, such as the sound of motor vehicles or fireworks, and to produce the output sounds at a comfortable loudness.

My relative tried the hearing aids on for a while. We were very satisfied and were quite happy to see her hear the world with the clarity that she has never had before.

We began to ask the audiologist about the price for these, and again we were amazed!! My relative is recommended to use a pair of these, for her left ear and right ear. Each of it cost 39,000 Thai Baht (approximately 1,000 US dollars). So...we would have to pay 78,000 Baht for a pair of these!!! I can't believe a tiny pair of hearing aids can be this expensive, compared to almost 50 Baht/meal that we pay for typical food here.

We had to roll back and study carefully about the alternatives we have for hearing aids. We were informed that the price of each one varies from 10,000 Bht for older analog model to 80,000-90,000 Bht for fancy digital ones.

I did a preliminary search and found some useful links:
Types of hearing aids
Fact sheet on choosing a hearing aid
DSP-type hearing aids
The hearing-aids Wikipedia
Sample price list of digital hearing aids
Nice Bernafon Symbio XT hearing aids
Hearing aid comparison chart

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