Pitch Class

A pitch names a particular high or low sound. A pitch class groups those pitches without regard to octave: C3, C4 and C5 are different pitches, but all belong to pitch class C. This distinction lets you discuss a chord's notes without specifying its exact register.

Twelve classes

In analysis based on twelve-tone equal temperament, enharmonic spellings also belong to the same class. C♯ and D♭ are two spellings of one pitch class, while C and C♯ are different classes. The twelve classes can be numbered from 0 to 11, with C = 0, C♯/D♭ = 1, and B = 11. After B, the numbering returns to 0 for C in the next octave.

This numerical convention does not mean that spelling is unimportant. C♯ and D♭ can have different musical functions, and tuning systems outside twelve-tone equal temperament need not make them identical in frequency.

Chords and voicings

C–E–G and E–G–C contain the same pitch classes, even when their notes occupy different octaves. Their inversion and voicing can still differ. Similarly, doubling C in a C major triad adds another sounding note, but no new pitch class.

Try playing C in three octaves, then C–E–G with different spacing. Listen for what stays recognizable while the actual pitches change.