Exactly - hearing is much more complicated than just noise sensitivity. For example, a somewhat underdiagnosed problems is issue with the frequency bins that the brain segments sound into for recognition deteriorating. Symptoms are - can hear just fine in a nice, uncluttered audio environment, say a test centre, but has issues if there is any significant background noise.

> Symptoms are - can hear just fine in a nice, uncluttered audio environment, say a test centre, but has issues if there is any significant background noise.

Also a problem if you're not a native speaker. I am fluent in English and have been able to watch movies without subtitles for 20 years at least, probably more.

But put me in a noisy bar and my error correction suffers a lot. Suddenly it's hard to follow a conversation that in my native language would be effortless.

The worst situation is listening to a loud video on bad speakers. Doesn't matter how much you crank the volume, people are hard to understand because the brain's error correction isn't good enough. Use a good speaker and turn down the volume, suddenly it's perfect.

Do any hearing aids frequency shift, or compress the frequency scale (e.g. just higher frequencies compressed down to lower frequencies so that voice tone stays constant and sibilants get shifted down into hearing range).

yes, I know Phonak hearing aids were doing that since about 2012. For some of our more severe hearing impaired patients it was a noticeable improvement in speech comprehension.

so a smart volume button

That pays attention to the environment and changes the volume (part of the spectrum perhaps?) that is what you're likely to be listening to.

This is of course a huge oversimplification, and aiming for it is probably what the industry is doing.

That is exactly what the tech does, automatically adjusts based on the amount of noise and speech in the environment. And going a step further, applying directional microphone control to better pick up sounds where the speech is.