We will follow the International Standards Organization (ISO) system for register designations. In that system, middle C (the first ledger line above the bass staff or the first ledger line below the treble staff) is C4. An octave higher than middle C is C5, and an octave lower than middle C is C3.

What key is C4?

This lesson is all about the musical note, middle C. This note is designated C4 in scientific pitch notation because of its position as the fourth C key on an 88-key piano.

Is C major high or low pitch?

In the major scale, there are eight notes going up the steps from bottom to top. These are the eight notes of the octave. On a C scale, the notes from low to high would be C, D, E, F, G, A, B, C.