Adjusting hearing aids using real-ear measurement

When my audiologist was adjusting my Oticon OPN 1s BTE hearing aids using real-ear measurements, at some point he found (and I noticed) that the aids weren’t “taking” the adjustments (i.e. the adjustments weren’t reflected in what the in-ear microphone was picking up). I found this a bit odd and pressed him for an explanation, which he gave:

Your question really gets at that “black box” concept I was telling you about last appointment. Many times the manufacturer does not want parameters adjusted beyond a certain point. They employ limiters behind-the-scenes. The most common reason they do this is to increase acceptance. When I make adjustments in the manufacturer software and the Real Ear Measurement does not reflect a change, it is likely that the software input data (the audiogram) has triggered some sort of limiter. Because your right and left audiograms are slightly different, it is possible that there are different limiters are employed for each ear. Again - these are proprietary things which we cannot access. But remember - we are trying to compare apples to oranges.

My question is: does this explanation make sense?

Coming from a fitter/audiologist that doesn’t understand the fitting software, yes. In my humble opinion.

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To me it means the aids do not have the correct recievers for your need. I had that issue with my OPN1 ITE hearing aids. I since have gone to the OPNS1 hearing aids with stronger recievers. And also the OPNS have better feedback control. The OPN1 aids do have issues with feedback and the software will limit the output of the aids to try and prevent feedback.
And in your case that is what it sounds like to me.

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If he’s not using NAL or DSL formulas but proprietary ones, then definitely it could be.

However, I don’t know if it’s possible to do REM for proprietary formulas. I’m not that familiar with the REM device.

There are some limits on hardware, definitely, as @cvkemp mentioned.

Also, this sound equalizer thing isn’t discrete thing. Yea we do have 6, 10, 16, 20, 24 handles and even more channels, but those handles aren’t able to adjust every frequency, and those in between are approximated.

Also, depending on the formula used for HA itself, if you lower gain for two nearby frequencies, REM still can show a bump between them and not shortest line, because yes, it depends on the implementation.

And we can’t enter exact values for gains per frequency, but we only can increase / decrease and that can affect nearby ones.

That behaviour can be described as limitation, but coming from IT industry, I’d lean more towards the ‘specific implementation’ and not ‘intentional limit so that you can’t get the best’. Yes, they might have algorithm that gives some ‘best’ which doesn’t work for you.

Join the club :joy:

So in short yeah, even if you say to HA to do something, it might not. However from what I saw, it will show that not doing anything in HA software. At least for cases I’ve tested on myself.

During REM and some proposals I’ve seen REM curve not reacting or reacting completely different from what we thought it’s going to happen.

But, yes, if we’re not talking about shape of those wave lines, but how much gain can be given or reduced, then stronger receiver or closing mold/dome would be my first thing to try out for adding, or opening the dome for reducing.

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“Stronger” receivers means “more sensitive” receivers?

Nope, those able to send more power/gain.

Receiver is speaker in HA terms.

He’s broadly correct, with a slight caveat.

The output graphs he’s seeing on the REM are a better reflection of the actual SPL in your ear than the fitting screen on the manufacturer software. However, that assumes you are putting in the right stimulus levels.

My preferred measure is REAR - real ear aided response, with normal speech inputs, not some dodgy noise mechanism. If your aid is clever enough to work out the input signal IS noise, whatever you turn the gain up to, the aid will ignore the signal.