The wester music has 12 notes today.
Use # to indicate that we’re ascending. Conversely, using b to indicate that we’re descending.
From a C to higher or lower C, it calls a register(c3 – > c4 = 3rd register). Also, C to the next higher or lower C calls octave.
C4 = 4th register = middle C
G6 means a particular G in the C6 – > C7