Pitches and Pitch Classes

A pitch is a distinct tone sung or played by an instrument. Pitches are caused by the speed of sound waves vibrating through the air. The faster sound waves vibrate, the higher the pitch. The slower they vibrate, the lower the pitch.

When a pitch’s sound waves are twice as fast as another pitch, those two pitches are separated by what is called an octave. Because these two pitches sound very similar, we give them the same name—you may have noticed that multiple pitches on the treble and bass clefs have the same name. For example, because the third space of the treble clef is an octave away from middle C, we also call this pitch C. All the pitches with the same letter name belong to the same pitch class. Middle C and every C above or below it all belong to the pitch class C.

To differentiate between pitches of the same pitch class, we attach them with a number called an octave number. This starts on the piano with its lowest C, called “C1.” Each octave above C1 raises the octave number by one. Middle C is the fourth C on the piano, so its pitch name is C4.