- Set (music)
A set (pitch set, pitch-class set, set class, set form, pitch collection) in music theory, as in mathematics and general parlance, is a collection of objects. In musical contexts the term is traditionally applied most often to collections of pitches or pitch-classes, but theorists have extended its use to other types of musical entities, so that one may speak of sets of durations or timbres, for example.
A time-point set is a duration set where the distance in time units between attack points, or time-points, is the distance in semitones between pitch classes .
A set by itself does not necessarily possess any additional structure, such as an ordering. Nevertheless, it is often musically important to consider sets that are equipped with an order relation (called segments); in such contexts, bare sets are often referred to as "unordered", for the sake of emphasis. 
In the theory of serial music, however, some authors (notably Milton Babbitt) use the term "set" where others would use "row" or "series", namely to denote an ordered collection (such as a twelve-tone row) used to structure a work. These authors speak of "twelve tone sets", "time-point sets", "derived sets", etc. (See below.) This is a different usage of the term "set" from that described above (and referred to in the term "set theory").
For these authors, a set form (or row form) is a particular arrangement of such an ordered set: the prime form (original order), inverse (upside down), retrograde (backwards), and retrograde inverse (backwards and upside down) .
B B♭ D E♭ G F♯ G♯ E F C C♯ A
Represented numerically as the integers 0 to 11:
0 11 3 4 8 7 9 5 6 1 2 10
The first set (B B♭ D) being:
0 11 3 prime-form, interval-string = <-1 +4>
The second set (E♭ G F♯) being the retrograde-inverse of the first, transposed up one semitone:
3 11 0 retrograde, interval-string = <-4 +1> mod 12 3 7 6 inverse, interval-string = <+4 -1> mod 12 + 1 1 1 ------ = 4 8 7
The third set (G♯ E F) being the retrograde of the first, transposed up (or down) six semitones:
3 11 0 retrograde + 6 6 6 ------ 9 5 6
And the fourth set (C C♯ A) being the inverse of the first, transposed up one semitone:
0 11 3 prime form, interval-vector = <-1 +4> mod 12 0 1 9 inverse, interval-string = <+1 -4> mod 12 + 1 1 1 ------- 1 2 10
Each of the four trichords (3-note sets) thus displays a relationship which can be made obvious by any of the four serial row operations, and thus creates certain invariances. These invariances in serial music are analogous to the use of common-tones and common-chords in tonal music.
The fundamental concept of a non-serial set is that it is an unordered collection of pitch classes (Rahn 1980, 27). The normal form of a set is the most compact ordering of the pitches in a set. Tomlin defines the "most compact" ordering as the one where, "the largest of the intervals between any two consecutive pitches is between the first and last pitch listed". For example, the set (0,2) (a major second) is in normal form while the set (0,10) (a minor seventh, the inversion of a major second) is not, its normal form being (10,0).
Rather than the "original" (untransposed, uninverted) form of the set the prime form may be considered the either the normal form of the set or the normal form of its inversion, whichever is more tightly packed.Prime Forms and Vectors of Pitch-Class Sets
Though set theorists usually consider sets of equal-tempered pitch classes, it is possible to consider sets of pitches, non-equal-tempered pitch classes, rhythmic onsets, or "beat classes" (Warburton 1988, 148; Cohn 1992, 149).
Two-element sets are called dyads, three-element sets trichords (occasionally "triads", though this is easily confused with the traditional meaning of the word triad). Sets of higher cardinalities are called tetrachords (or tetrads), pentachords (or pentads), hexachords (or hexads), heptachords (heptads or, sometimes, mixing Latin and Greek roots, "septachords"—e.g., Rahn 1980, 140), octachords (octads), nonachords (nonads), decachords (decads), undecachords, and, finally, the dodecachord.
- Schuijer, Michiel (2008). Analyzing Atonal Music: Pitch-Class Set Theory and Its Contexts. ISBN 978-1-58046-270-9.
- ^ Whittall, Arnold (2008). The Cambridge Introduction to Serialism, p.165. New York: Cambridge University Press. ISBN 978-0-521-68200-8 (pbk).
- ^ a b Wittlich, Gary (1975). "Sets and Ordering Procedures in Twentieth-Century Music", Aspects of Twentieth-Century Music, p.475. Wittlich, Gary (ed.). Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0-13-049346-5.
- ^ Wittlich (1975), p.476.
- ^ Whittall (2008), p.127.
- ^ Morris, Robert (1987). Composition With Pitch-Classes: A Theory of Compositional Design, p.27. Yale University Press. ISBN 0-300-03684-1.
- ^ See any of his writings on the twelve-tone system, virtually all of which are reprinted in The Collected Essays of Milton Babbitt, S. Peles et. al, eds. Princeton University Press, 2003. ISBN 0-691-08966-3.
- ^ Wittlich (1975), p.474.
- ^ Whittall (2008), p.97.
- ^ a b Tomlin, Jay. "All About Set Theory: What is Normal Form?", JayTomlin.com.
- ^ Tomlin, Jay. "All About Set Theory: What is Prime Form?", JayTomlin.com.
- "Set Theory Calculator", JayTomlin.com. Calculates normal form, prime form, Forte number, and interval class vector for a given set and vice versa.
Pitch sets by cardinality
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