Pitch class
Set of all pitches that are a whole number of octaves apart / From Wikipedia, the free encyclopedia
In music, a pitch class (p.c. or pc) is a set of all pitches that are a whole number of octaves apart; for example, the pitch class C consists of the Cs in all octaves. "The pitch class C stands for all possible Cs, in whatever octave position."[1] Important to musical set theory, a pitch class is "all pitches related to each other by octave, enharmonic equivalence, or both."[2] Thus, using scientific pitch notation, the pitch class "C" is the set
- {Cn : n is an integer} = {..., C−2, C−1, C0, C1, C2, C3 ...}.
![{\n\\override Score.TimeSignature #'stencil = ##f\n\\relative c' {\n \\clef treble \\key c \\major \\time 4/4\n <c c'>1\n} }\n](http://upload.wikimedia.org/score/c/k/ckvjnh1hmcrf71k9diwfumyxwmm0ceq/ckvjnh1h.png)
![{\n\\override Score.TimeSignature #'stencil = ##f\n\\new PianoStaff <<\n\\new Staff \\relative c' {\n \\clef treble \\key c \\major \\time 4/4\n <c' c' c'>1 \\bar "|."\n}\n\n\\new Staff \\relative c' {\n \\clef bass \\key c \\major \\time 4/4\n <c c, c, c,>1\n} >> }\n](http://upload.wikimedia.org/score/o/c/oc9zzbd2uvdnf77uodfo4bfk7ci2ffk/oc9zzbd2.png)
Although there is no formal upper or lower limit to this sequence, only a few of these pitches are audible to humans. Pitch class is important because human pitch-perception is periodic: pitches belonging to the same pitch class are perceived as having a similar quality or color, a property called "octave equivalence".
Psychologists refer to the quality of a pitch as its "chroma".[3] A chroma is an attribute of pitches (as opposed to tone height), just like hue is an attribute of color. A pitch class is a set of all pitches that share the same chroma, just like "the set of all white things" is the collection of all white objects.[4]
In standard Western equal temperament, distinct spellings can refer to the same sounding object: B♯3, C4, and D4 all refer to the same pitch, hence share the same chroma, and therefore belong to the same pitch class. This phenomenon is called enharmonic equivalence.