Do they have an app with an equalizer that ets you adjust the level of each frequency?
Yes, you can do that with your smartphone app and save it.
The only thig about it is it’s not saved in the device itself, just on your phone. So every time you turn off your aids they revert back to their permanent program from the audiologist’s data. You can reload any of 4 programs you store for different locations, like ‘WORK’, ‘RESTAURANT’, SPORTS GAME’ etc...........
And each ear is separate.................
Why hearing aids are 96 frequencies. I get a detailed hearing test and then the audiologist adjusts the individual frequencies according to the results of what I can hear at those individual frequencies.
So in answer your question it’s done by the audiologist
I’ve been working with the same guy for 8 years and I think there’s a bit of an art to the adjustment