pitch class
The set of all pitches sharing the same letter name regardless of octave, reduced to one of twelve chromatic values
In Depth
A pitch class collapses octave equivalence: all Cs in every register belong to pitch class C, represented numerically as 0 in integer notation (with C# = 1, D = 2, etc.). This abstraction is fundamental to post-tonal theory, where octave register is often treated as a secondary parameter. Pitch-class thinking enables analysis of music where traditional note names and key relationships do not apply, and forms the basis of twelve-tone and serial techniques.
The concept of pitch class was implicit in twelve-tone technique from its invention, but the formal mathematical treatment did not appear until the 1960s.