If you cannot hear 4800 Hz, this probably indicates a serious damage then, for usually, as far as I read, 8000 Hz is the minimum of what healthy old people should hear, even at higher ages above 80. And as far as I kow you still have not hit that age mark, eh?
Having pulled those guitar strings too hard, maybe? My father has been professional musician, too (bassoon), having the brass players blowing right in his neck in all those years (thats the sitting order in a sinfonic orchestra), he has damaged ears now, too.
There are videos at youtube that mark biological age and associated frequencies. When we become older, we all loose the ablity to listen to the high frequencies, we start at around 20 Khz, and it then drops to around 8 KHz at high age. Somebody who can merely hear 12 KHz, is assumed to be below 50 years, 15 KHz represents below 40 years, 16 KHz is typical for ages below 30, 18 KHz equals below 20, 19 KHz is below 15 years. I am 50, but can hear 15 KHz still, so I am doing well in these regards.
The times when I was even hearing the low frequency calls of bats however are over since long (bats can call and listen in the range of low 20s of KHz up to 200 KHz).