I read this report from Barrett Media and found it quite interesting. The writer has solid credentials.

Too much new music in one hour seems to be a listener killer.

I have read some of the regulars on this board mention CHR stations are going deeper into their library. Songs which would naturally drop off the charts of a station, seem to have a longer shelf life.

WXRT-FM surrounds the new music it plays with familiar music. It's one of the few triple-A formats which plays as much classic rock as they do and it's a ratings and revenue success.