- This article is about multiplication in music; for multiplication in mathematics see multiplication.
The mathematical operations of multiplication have several applications to music. Other than its application to the frequency ratios of intervals (e.g., Just intonation, and the twelfth root of two in equal temperament), it has been used in other ways for twelve-tone technique, and musical set theory. Additionally ring modulation is an electrical audio process involving multiplication that has been used for musical effect.
A multiplicative operation is a mapping in which the argument is multiplied (Rahn 1980, 53). Multiplication originated intuitively in interval expansion, including tone row order number rotation, for example in the music of Béla Bartók and Alban Berg (Schuijer 2008, 77–78). Pitch number rotation, Fünferreihe or "five-series" and Siebenerreihe or "seven-series", was first described by Ernst Krenek in Über neue Musik (Krenek 1937; Schuijer 2008, 77–78). Princeton-based theorists, including "James K. Randall , Godfrey Winham , and Hubert S. Howe  were the first to discuss and adopt them, not only with regards to twelve-tone series" (Schuijer 2008, 81).
Pitch class multiplication modulo 12 
When dealing with pitch class sets, multiplication modulo 12 is a common operation. Dealing with all twelve tones, or a tone row, there are only a few numbers which one may multiply a row by and still end up with a set of twelve distinct tones. Taking the prime or unaltered form as P0, multiplication is indicated by , being the multiplicator:
The following table lists all possible multiplications of a chromatic twelve-tone row:
|M||M × (0,1,2,3,4,5,6,7,8,9,10,11) mod 12|
Note that only M1, M5, M7, and M11 give a one to one mapping (a complete set of 12 unique tones). This is because each of these numbers is relatively prime to 12. Also interesting is that the chromatic scale is mapped to the circle of fourths with M5, or fifths with M7, and more generally under M7 all even numbers stay the same while odd numbers are transposed by a tritone. This kind of multiplication is frequently combined with a transposition operation. It was first described in print by Herbert Eimert, under the terms "Quartverwandlung" (fourth transformation) and "Quintverwandlung" (fifth transformation) (Eimert 1950, 29–33), and has been used by the composers Milton Babbitt (Morris 1997, 238 & 242–43; Winham 1970, 65–66), Robert Morris (Morris 1997, 238–39 & 243), and Charles Wuorinen (Hibbard 1969, 157–58). This operation also accounts for certain harmonic transformations in jazz (Morris 1982, 153–54).
Thus multiplication by the two meaningful operations (5 & 7) may be designated with M5(a) and M7(a) or M and IM (Schuijer 2008, 77–78).
- M1 = Identity
- M5 = Cycle of fourths transform
- M7 = Cycle of fifths transform
- M11 = Inversion
- M11M5 = M7
- M7M5 = M11
- M5M5 = M1
- M7M11M5 = M1
Pitch multiplication 
Pierre Boulez (1971,[page needed]) described an operation he called pitch multiplication, which is somewhat akin[clarification needed] to the Cartesian product of pitch class sets. Given two sets, the result of pitch multiplication will be the set of sums (modulo 12) of all possible pairings of elements between the original two sets. Its definition:
For example, if multiplying a C major chord with a dyad containing C,D , the result is:
In this example, a set of 3 pitches multiplied with a set of 2 pitches gives a new set of 3 × 2 pitches. Given the limited space of modulo 12 arithmetic, when using this procedure very often duplicate tones are produced, which are generally omitted. This technique was used most famously in Boulez's 1955 masterpiece Le marteau sans maître, as well as in his Third Piano Sonata, Pli selon pli, Eclat (and Eclat multiples), Figures-Doubles-Prisms, Domaines, and Cummings ist der Dichter, as well as the withdrawn choral work, Oubli signal lapidé (1952) (Koblyakov 1990; Heinemann 1993 and 1998).
Mirror form of multiplication 
Herbert Eimert described what he called the "eight modes" of the twelve-tone series, all mirror forms of one another. The inverse is obtained through a horizontal mirror, the retrograde through a vertical mirror, the retrograde-inverse through both a horizontal and a vertical mirror, and the "cycle-of-fourths-transform" or Quartverwandlung and "cycle-of-fifths-transform" or Quintverwandlung obtained through a slanting mirror (Eimert 1950, 28–29). With the retrogrades of these transforms and the prime, there are eight permutations.
Furthermore, one can sort of move the mirror at an angle, that is the 'angle' of a fourth or fifth, so that the chromatic row is reflected in both cycles. . . . In this way, one obtains the cycle-of-fourths transform and the cycle-of-fifths transform of the row. (Eimert 1950, 29; trans. Schuijer 2008, 81)
- Antokoletz, Elliott. 1993. "Middle Period String Quartets". In The Bartok Companion, edited by Malcolm Gillies, 257–77. London: Faber and Faber. ISBN 0-571-15330-5 (cased); ISBN 0-571-15331-3 (pbk).
- Boulez, Pierre. 1971. Boulez on Music Today. Translated by Susan Bradshaw and Richard Rodney Bennett. Cambridge, Mass.: Harvard University Press. ISBN 0-674-08006-8.
- Eimert, Herbert. 1950. Lehrbuch der Zwölftontechnik. Wiesbaden: Breitkopf & Härtel.
- Heinemann, Stephen. 1993. "Pitch-Class Set Multiplication in Boulez's Le Marteau sans maître. D.M.A. diss., University of Washington.
- Heinemann, Stephen. 1998. "Pitch-Class Set Multiplication in Theory and Practice." Music Theory Spectrum 20, no. 1 (Spring): 72-96.
- Hibbard, William. 1969. "Charles Wuorinen: The Politics of Harmony". Perspectives of New Music 7, no. 2 (Spring-Summer): 155–66.
- Howe, Hubert S. 1965. “Some Combinational Properties of Pitch Structures.” Perspectives of New Music 4, no. 1 (Fall-Winter): 45–61.
- Koblyakov, Lev . 1990. Pierre Boulez: A World of Harmony. Chur: Harwood Academic Publishers. ISBN 3-7186-0422-1.
- Krenek, Ernst. 1937. Über neue Musik: Sechs Vorlesungen zur Einführung in die theoretischen Grundlagen. Vienna: Ringbuchhandlung.
- Morris, Robert D. 1982. Review: "John Rahn, Basic Atonal TheoryNew York: Longman, 1980". Music Theory Spectrum 4:138–54.
- Morris, Robert D. 1997. "Some Remarks on Odds and Ends". Perspectives of New Music 35, no. 2 (Summer): 237–56.
- Rahn, John. 1980. Basic Atonal Theory. Longman Music Series. New York and London: Longman. Reprinted, New York: Schirmer Books; London: Collier Macmillan, 1987.
- Randall, James K. 1962. "Pitch-Time Correlation". Unpublished. Cited in Schuijer 2008, 82.
- Schuijer, Michiel. 2008. Analyzing Atonal Music: Pitch-Class Set Theory and Its Contexts. Eastman Studies in Music 60. Rochester, NY: University of Rochester Press. ISBN 978-1-58046-270-9.
- Winham, Godfrey. 1970. “Composition with Arrays”. Perspectives of New Music 9, no. 1 (Fall-Winter): 43–67.
Further reading 
- Morris, Robert D. 1977. "On the Generation of Multiple-Order-Function Twelve-Tone Rows". Journal of Music Theory 21, no. 2 (Autumn): 238–62.
- Morris, Robert D. 1982–83. "Combinatoriality without the Aggregate". Perspectives of New Music 21, nos. 1 & 2 (Autumn-Winter/Spring-Summer): 432–86.
- Morris, Robert D. 1990. "Pitch-Class Complementation and Its Generalizations". Journal of Music Theory 34, no. 2 (Autumn): 175–245.
- Starr, Daniel V. 1978. "Sets, Invariance, and Partitions." Journal of Music Theory 22, no. 1:1–42.