(Fr. octave; Ger. Oktave; It. ottava; Gk. diapasōn;; Sp. octava).
The interval between any two notes that are seven diatonic scale degrees apart (e.g. c–c', d–d'). The term usually implies ‘perfect octave’, which is the sum of five whole tones and two diatonic semitones; however it also covers the augmented octave, which is the sum of a perfect octave and a chromatic semitone (e.g. c–c', d–d'), and the diminished octave, which is a perfect octave less a chromatic semitone (e.g. c–c', d–d'). Acoustically the octave is the simplest of all intervals, giving a frequency ratio of 2:1 (a 1:2 ratio of string length); it is also the interval between a note and its first harmonic overtone.
To Western and most non-Western musicians, two notes an octave apart are in a sense alike, being different only in their relative registers and often seeming to blend into one another. This acoustical phenomenon has made the division of the frequency spectrum into octaves fundamental to both the understanding and the notation of music. The ancient Greeks, who recognized this phenomenon, called the octave harmonia, later diapasōn; Ptolemy, writing in the 2nd century, distinguished the octave from the other perfect intervals, calling it homophōnia (the 5th and 4th were called symphōnia). In the notation developed during the Middle Ages, notes an octave or two octaves apart were given the same letter name; and it was the species of octave (i.e. the arrangement of tones and semitones in an eight-note diatonic scale) that determined the Mode to which that scale belonged. Because of its acoustical properties the octave plays a significant role in the construction and playing of instruments, particularly keyboard and woodwind instruments (e.g. those that have ‘octave keys’), and is of fundamental importance to the concept of Register, both in a theoretical sense and as it concerns instruments.
See under Organ stop.
Non-musical uses of the term, which may occasionally be found in musical contexts, include the eighth day (i.e. exactly a week) after any feast day, or the day of a feast and the entire week following it; also the first eight lines of a sonnet.
See also Consecutive fifths, consecutive octaves; Diapason (i); Doubling; Hidden fifths, hidden octaves.
A type of signal processing unit that divides or multiplies the frequency of a signal by a factor of two, to give parallel octaves below or above the note being produced by an instrument. The unit is often operated by means of a foot-pedal. SeeElectric guitar, §2.
By analogy with the sextet, septet and nonet, the term ‘octet’, first used at the beginning of the 19th century, denotes a composition in the nature of chamber music for eight solo instruments. The term was first used by Prince Louis Ferdinand of Prussia, whose Octet op.12 (c1800, published 1808) has a central piano part and remained almost unique of its kind. Further works with piano were written by Ferdinand Ries (op.128, 1818), Anton Rubinstein (op.9, 1856) and Paul Juon (op.27, 1907); through the number of instruments alone they all tend to a more concertante style. Nor did the works for mixed wind and string instruments by Peter Winter (c1812), Spohr (op.32, 1814), Reicha (op.96, c1817) and Hindemith (1957–8), each using a different combination, have any lasting influence on the genre. Only the ensemble chosen by Schubert for his Octet (d803), written in 1824 but not published (posthumously) until 1853, developed in the late 19th century into what is still regarded as the standard combination of instruments: clarinet, horn, bassoon, two violins, viola, cello and double bass. Schubert's octet, itself stimulated by Beethoven's extremely successful Septet op.20, inspired many composers to write works for the same ensemble, not least for practical performance reasons: they have included Hugo Kaun (op.26, published in error as op.34, 1891), Ferdinand Thieriot (op.62, 1893), Heinrich Molbe (op.20, 1897), Howard Ferguson (op.4, 1933), Egon Wellesz (op.67, 1949, with english horn), Boris Blacher (1965), Iannis Xenakis (Anaktoria, 1969), Rudolf Kelterborn (Oktett 1969, 1970), Siegfried Matthus (1970), Jean Françaix (A HUIT, 1972), Isang Yun (1978) and Dieter Schnebel (raum-zeit y, arranged for eight instruments 1992–3).
The string octet for four violins, two violas and two cellos, beginning with Mendelssohn's ingenious op.20 (1825, published 1833), formed a separate tradition comprising works by Niels Gade (op.17, 1848), Carl Schuberth (op.23, 1848), Johan Svendsen (op.3, 1865–6), Carl Grädener (op.49, 1870), Joachim Raff (op.176, 1872), Woldemar Bargiel (op.15a, 1877), Hermann Grädener (op.12, 1881), Reyngol'd Glier (op.5, 1900), Enescu (op.7, 1900), Ferdinand Thieriot (op.78, 1903), Bruch (1920) and Shostakovich (Two Pieces op.11, 1924–5). In some of the older compositions the influence of the extremely light, almost scurrying inflection of Mendelssohn's Scherzo can be felt.
Spohr developed an entirely different technical concept of setting with his four double quartets (opp.65, 77, 87 and 136, 1823–47); their antiphonal structure was suggested by a work by Andreas Romberg that remained fragmentary. Similar compositions were written by Nikolay Afanas'yev (Housewarming and Le souvenir) and Mario Peragallo (Music for Double Quartet, 1948). Darius Milhaud's Octet is a curiosity: the composer specified that his 14th and 15th string quartets op.291 (1948–9) may be played separately or, simultaneously, as an octet.
Wind compositions for eight instruments (usually two oboes, two clarinets, two horns and two bassoons), traditionally entitled partita, serenade, cassation, etc., because they were played in the open air, were written for indoor performance as chamber music during the 19th century and termed octets: they included works by Beethoven (op.103, ?1792–3, published 1830), Franz Lachner (op.156, 1850, published 1872), Louis Théodore Gouvy (op.71, published 1882) and Carl Reinecke (op.216, c1892). Entirely different combinations of eight wind instruments are used in Stravinsky's Octet and Varèse's Octandre (both 1923), two important 20th-century compositions.