Thanks to Scott and BradMZ for replying to me and I can finally, accurately describe the real problem I have. I can only hear the difference on acoustic pianos and the problem occurs at E4 on the PX-5S. From their downwards, a brighter sound is heard. If I select Piano mono1, it plays fine on high notes and all the way down to F4, then it plays the mono2 tone from E4 downwards. Same applies with piano sounds (i,e GrPno Studio with GrPno Modern). A an experiment, I created a stage setting using GM1 piano in zone 1 (C- to E4) and GM2 piano in zone 2 (F4 to G9). The result was that it played as a GM2 piano for the full range. Have I messed some settings at some time. or have I got a faulty PX-5S