That does not surprise me since the entire clinical definition of hearing loss is based on a 125Hz-8000Hz pure tone audiogram. It's probably safe to assume people with very high pitch tinnitus have an undocumented hearing loss.
I came across some people with tinnitus who don't have loss even on an extended audiogram, but it's a minority.
I really don't understand why this isn't studied more. Audiologists keep quoting the same stupid numbers even though when pressed they must admit the data is flawed and more research is needed. How hard would it be to let a Ph.D. candidate run a study in a tinnitus clinic? All it takes is 5 extra minutes in the audio booth.
I've seen a preliminary study suggesting that when performing an extended audiogram, the group "without hearing loss" suddenly shrinks by a lot.
What about those with hearing loss and no tinnitus?
According to Dr. De Ridder, they must have something in the brain that does not try to compensate for hearing loss by mal-adapting and introducing noise in the system.