What are "Channels" and why are more better?

A channel is just a small frequency band, so covering a whole number of discrete frequencies.

The reason for having a few rather than many is for reasons of practicality and need.

The practicality is that if you want a very large number of channels then you would have to have a very complex and power-hungry digital processor in the hearing aid. This would be much more power-hungry, expensive and physically larger. It’s just not practical.

And also adjusting so many channels would be difficult and time-consuming, so in practice the audiologist would need to adjust them in groups.

And further most people would never notice the difference. Given a choice, they would go for the cheaper smaller hearing aid with the better battery life.

You can build an audiogram for yourself if a very large number of measurements and then do it again with 20 spot measurements and look at the two different graphs. Remembering that generally people who don’t know what they are listening for won’t notice a change in a channel of less than a couple of dB, you would probably find that the two audiograms are pretty well the same.

Thanks - ok, so 128 channels is the same as 128 frequency bands. I was at a lucid hearing center recently, and she mentioned 128 channels, but I noticed the software could only fine tune, or create a target prescription, for about 10 of those frequencies. I wonder how Lucid “uses” 128 channels? perhaps in some kind of autosense mode?

Sorry I don’t know. It’s not a brand that means anything to me. Also their use of the term channels sounds quite dubious to me. Probably they are best avoided.