They are just analog hearing aids inside, however. Each band could have its own amplification, compression limiting, or dynamic range settings. A simple version of this could be an aid with two bands, one high frequency and one low frequency. The aid might have automatic volume controls set to cut the amplification in the high frequency band in the presence of loud noise without changing the amplification of the low frequency band. This would be good for many noisy situations.
Some hearing aids have more than one group of settings.
A simple one-program hearing aid can be set for the listening situation that bothers you the most, or perhaps the one where you spend most of your time, such as near a noisy air conditioner in your office. Multiple-program hearing aids can be switched between programs whenever you like. For example, you might have one program for quiet conversation or music, and another for noisy situations where communication is difficult. Some hearing aids have many different programs. More programs are not necessarily better however, because switching between them and keeping track of which program you are using can be a bother.