Atetrad is a set of fournotes inmusic theory. When these four notes form atertian chord they are more specifically called aseventh chord, after thediatonicinterval from theroot of thechord to its fourth note (in root position close voicing). Four-note chords are often formed of intervals other than thirds in 20th- and 21st-century music, however, where they are more generally referred to astetrads.[1] Musicologist Allen Forte in hisThe Structure of Atonal Music never uses the term "tetrad", but occasionally employs the wordtetrachord to mean any collection of fourpitch classes.[2] In 20th-century music theory, suchsets of four pitch classes are usually called "tetrachords".[3][4]
Anonymous (2001). "Tetrachord".The New Grove Dictionary of Music and Musicians, second edition, edited byStanley Sadie andJohn Tyrrell. London: Macmillan Publishers.
Forte, Allen (1985). "Pitch-Class Set Analysis Today".Music Analysis 4, nos. 1 & 2 (March–July: Special Issue: King's College London Music Analysis Conference 1984): 29–58.
Gamer, Carlton (1967). "Some Combinational Resources of Equal-Tempered Systems".Journal of Music Theory 11, no. 1:32–59.
Hanson, Howard (1960).Harmonic Materials of Modern Music: Resources of the Tempered Scale. New York: Appleton-Century-Crofts.
Roeder, John (2001). "Set (ii)".The New Grove Dictionary of Music and Musicians, second edition, edited by Stanley Sadie and John Tyrrell. London: Macmillan Publishers.
