Hearing Aid Curve for Music

They could do that from 250 Hz to 8 kHz, but you would hate it and depending on the loss it might damage your ears. Loudness is not linear like that.

You’re describing the test and fitting process. Test and recording is done in steps, and as it’s intended for speech it goes up to 8KHz. Similarly, hearing aids are made to provide boost up to 8~10KHz. The fitting is the boost applied where needed. The boost is applied, in the hearing aid, in ‘channels’ selections of the frequency range and the number/span of those channels are model dependent.

Generally speaking, hearing aids only try to give you back a third of your missing sound sensitivity.

The basic reason for this is that most hearing losses reduce your sensibly to low level sounds but don’t affect the maximum level you can hear without distortion or even damage.

So trying to correct the frequencies where you have a loss is by no means all of the story.