What is the objective of hearing aid fitting software

[mthomas]

Hello Everyone,


I am on a quest to comprehend the functionalities of hearing aids and their fitting software. We all know their primary purpose is to improve our hearing, but I'm eager to understand the mechanics behind it. For instance, in my right ear, I need a 8000 Hz tone to be amplified to 95db before I can acknowledge it in an audiology test.


Naturally, on my Audiogram, there's an X mark at 95 on the 8000 axis. Now, when it comes to the hearing aid, does it mean we need it to boost that particular frequency gain by 95db? Similarly, if it takes 40db for me to hear a 1000 Hz tone, does the hearing aid amplify that frequency gain by 40db?


I pose these questions because I'm curious about the audiologist's method during a hearing aid fitting. Are they adjusting the gain for each frequency according to that loss to enable you to hear? While I acknowledge the complexity of audiology and respect that professionals spend years mastering it, personal circumstances make access to an audiologist difficult for me. Thus, I aim to program my own hearing aid. However, I want to have a clear understanding of what I'm instructing the fitting software to do, instead of making arbitrary adjustments.


Can anyone shed light on this process, or share the key objective here? I am eager to grasp this concept rather than rely on trial and error adjustments.

Much Appreciated.
M

 

[pvc]

Well, I don't know the answer to your question? I don't even know how to find an answer to your question? But it's not all about decibels, for example gain is applied differently for soft, moderate, and loud sounds. So there's that.

The fitting software calculates the Rx/Prescription based on many things and the fitting formula can also be changed allowing → many-choices. This Utube video link has some basics → Basic Tuning in Connexx 9 | Signia Hearing Aids.

You could try some experimental testing. Read a DIY School Hearing Aids PDF file named (01 Exploring the Fitting Software) and learn how to explore the fitting software for whatever manufacturer you choose. They are all a bit different.

Here's an example using the SIMULATE feature of Oticon's Genie 2 for risk free testing of various scenarios; I created a client with normal hearing and proceeded to see what GAIN CONTROLS were prescribed. As you can see hardly any Gain is applied, ETA: Oops, I forgot to slide Gain control to #3. You could run a different test with a different hearing loss/Audiogram to compare the differences in gain.

 

[pvc]

For instance, in my right ear, I need a 8000 Hz tone to be amplified to 95db before I can acknowledge it in an audiology test.

If you get great results from Rx/Prescribed settings at 8000 Hz, then you will be able to hear those pesky birds. Which can sometimes be annoying. Hearing speech is maybe more important.

 

[pvc]

I know that this doesn't answer your question, and I know that typical hearing losses are not flat like in the Audiograms that I used. But for experimental purposes here are three gain comparisons for three Flat losses of (20 dB, 40 dB, 60 dB) for all frequencies.

 

[Volusiano]

I will supplement a few more things to what @pvc has already explained above. The fact that you need an amplification at 40 dB to be able to trigger your hearing at 1 KHz, for example, only makes your threshold hearing level to be at 40 dB, meaning that if there is an input signal at 5 dB, for example, maybe the hearing aid may amplify this 5 dB signal at 45 dB so that you can hear almost the equivalent of what a normal hearing person can hear this sound at 5 dB.

However, the amplification is not a linear relationship where you simply make the hearing aid add 40 dB to any signal at 1 KHz. There's also a limit to how loud of a sound you can tolerate at 1 KHz (it's called the max power output, or MPO for short). This MPO is measured as part of your audiometry test to get your audiogram. For example, if your MPO is 100 dB at 1 KHz, if there's a loud signal coming in at 80 dB, if the hearing aid linearly adds 40 dB to it, then that would pound your ear at 120 dB, 20 dB louder over the MPO limit that your ear can tolerate at 100 dB.

So the fitting rationale takes into account not just your hearing threshold level, but it also takes into account your MPO level at that frequency. Then it comes up with a formula that would compress the normal volume range of a normal hearing person between 0 dB to 120 dB into the tighter range that your hearing loss can detect AND tolerate. So in the case of 1 KHz sounds, a 1 dB sound input may be amplified to 41 dB for you ear, but sounds at 100 to 120 dB would not be amplified at all, because remember that your MPO is only at 100 dB, which is your upper range limit.

So the normal hearing range of 0-120 dB would be mapped into your tighter hearing loss range of 40-100 dB at 1 KHz. This mapping is divided into 3 sections, from soft sounds at 45 dB, medium sounds at 65 dB and loud sounds at 80 dB. and the amplification is stronger for soft sounds, not as strong for medium sounds, and even less strong for loud sounds. So by now, hopefully it should be already obvious to you that the fitting rationale prescribes an amplification formula that is not really linear at all. It's designed to amplify accordingly and appropriately at various levels of sound volumes, with your threshold hearing level (from your audiogram) and your MPO tolerance level (also from audiogram) as key parameters in its equation, with the overall goal of compressing the normal hearing range into your more limited hearing range. And it does it differently and automatically for the different frequency channels/bands in your hearing aids. This is called Wide Dynamic Range Compression (WDRC).

Below is an illustration of what an example of a WDRC may look like. Of course it varies depending on your hearing loss. But the more severe the hearing loss, the tighter/more limited the impaired range of hearing becomes. And if this tighter impaired range gets too tight, it's easier to lose the ability to differentiate the volume levels, and therefore limiting the subtleties and nuances that the varying volumes can be discerned by your limited hearing.

As complicated as the above explanation may seem to be, it's actually even more complicated than that. The fitting rationale may add other parameters and factors into its formula to adjust for and deal with other things as well. For example, some formula may put focus on speech understanding (specifically the standard ones like DSL or NAL-NL1 and NAL-NL2. Yet other formula like the proprietary ones from each brand may put focus on yet other things, like how to deal with different types of hearing losses (ski-slope, reverse ski-slope, cookie bite, reverse cookie-bite, etc). Proprietary formula may also factor in the specifics in the designs of that hearing aid's brand and models, none of which would be known to standard fitting rationales and these standard rationales may have to make assumptions about hearing aids that may or may not be true to a certain brand/model. So I'm going to stop going further than that here because hopefully you'll have appreciated by now that it's a very complex endeavor to come up with how to amplify for a hearing loss.

 

[pvc]

Very excellent post Mr V !!

If you are not too shy and would like to contribute to the knowledge collection in DIY School Hearing Aids, I would like to capture this knowledge in a DIY School Hearing Aids PDF File named (How Hearing Aid Gain Fits Your Loss) or whatever title you wish to use.

I have started a template MS-Word file (which I can provide upon request) or you can simply provide the title/subtitles/text/images and I will assemble the PDF File for inclusion into DIY School.

Below is the template I came up with.

 

[Volusiano]

Hi @pvc , I think what I said above kinda captured pretty much what I would have written for that section in your DIY school anyway, so feel free to just go ahead and capture its entirety into the text, really no need for editing in my opinion. Perhaps preface it with a short snippet of the OP's original question to provide context into the answer I gave above. Of course, feel free to edit and rearrange what I wrote into whatever appropriate format as you see fit. Thanks!

 

[pvc]

Thanks, Will do. Helpful information such as this tend to get buried in forum discussions and then drift into oblivion simply because the dated posted is old. Give me a few ̶d̶a̶y̶s̶ / hours.

 

[Volusiano]

Excellent point there, Mr. @pvc ! Thank YOU for taking the time to compile and document valuable DIY and even general information so that they don't get lost and buried in the midst of things. Sometimes even if it can be made into a sticky, stickies don't necessarily get organized into appropriate places like how you organize your DIY School topics.

 

[pvc]

Announcing a New DIY School Hearing Aids PDF File (How Hearing Aid Gain Fits Your Loss) is now available.

 

[SayAgain]

MPO is measured as part of your audiometry

MPO is an adjustable setting of hearing aids; it's not part of audiometry.

So, MPO -> UCL -- Uncomfortable Loudness, or LDL -- Loudness Discomfort Level. I think "UCL" is the abbreviation generally used on hearing test reports.

 

[pvc]

HMm; I think you are correct that it is not part of the audiogram/measurements. Yes the UCL is measured (tell me when this is way too loud)!

From → this reference I believe that MPO is the capacity of the hearing aid model, or in the case of RICs/RITEs the capacity of the hearing aid receiver. Even though MPO can be adjusted, it is not an adjustment/change normally used for mild/moderate hearing aid losses.

 

[pvc]

Made up a client for testing using the SIMULATE feature of Genie2. Yes, the MPO changes when you switch to a different hearing aid model or in the case of RITEs, a different receiver. The first gain settings are for RITEs with 105 receivers and the second is a BTE (same client/same audiogram);

 

[pvc]

Changed/Updated the DIY School Hearing Aids PDF File (How Hearing Aid Gain Fits Your Loss) as follows;

The MPO setting may be Rx’d/Prescribed (higher or lower) depending on your hearing aid models, or in the case of RIC/RITE hearing aids, depending on the power of your receivers. The Rx’d/Prescribed MPO functions as a gain limiter, for example, if your MPO is 100 dB at 1 KHz, when there's a loud signal coming in at 80 dB, if the hearing aid linearly adds 40 dB to it, then that would pound your ear at 120 dB, 20 dB louder over the MPO limit that your ear can tolerate at 100 dB.B.

Mr V/ @Volusiano; If you approve of the wording, then we are all done. Or let me know if you prefer other wording.
Thanks for the Tip @SayAgain