Sir aap ne video acchi banai,,,,Par C4 ka octave galat bataya hai,,,,,, Keyboard 5 octave hota hai lekin setting 7 octave ki hoti hai tone ki,,,,ek octave right main or ek octave left main hota to hai but hamain dikhai sirf 5 hi dete hain to,,,,, 5 octave keyboard ka left side se Frist white note C2 hota hai fir C3 or C4 center hota hai ,,,,,,lekin aapne C5 ko C4 bataya hai