Ionisation (1929–1931) is a musical composition by Edgard Varèse written for thirteen percussionists. It was among the first concert hall compositions for percussion ensemble alone, although Alexander Tcherepnin had composed an entire movement for percussion alone in his Symphony No. 1 from 1927. The premiere was at Carnegie Chapter Hall, an annex to New York City's Carnegie Hall, on March 6, 1933, conducted by Nicolas Slonimsky, to whom the piece was later dedicated. One critic described the performance as "a sock in the jaw."
The instrumentation is the following:
3 bass drums (medium, large, very large), 2 tenor drums, 2 snare drums, tarole (a kind of piccolo snare drum), 2 bongos, tambourine, field drum, crash cymbal, suspended cymbals, 3 tam-tams, gong, 2 anvils, 2 triangles, sleigh bells, cowbell, chimes, glockenspiel, piano, 3 temple blocks, claves, maracas, castanets, whip, güiro, high & low sirens, and a lion's roar.
Ionisation features the expansion and variation of rhythmic cells, and the title refers to the ionization of molecules. As the composer later described, "I was not influenced by composers as much as by natural objects and physical phenomena." (Schuller 1965, p. 34) Varèse also acknowledged the influence of the Italian Futurist artists Luigi Russolo and Filippo Tommaso Marinetti in the composition of this work.
Both Chou Wen-Chung and Jean-Charles François have analyzed the structure and timbre features of Ionisation in detail. András Wilheim has noted that only the last 17 measures of Ionisation include musical tones of the "traditional tonal system", where any five successive chords contain the 12 tones of the chromatic scale.
Frank Zappa often claimed that Ionisation inspired him to pursue a career in music. It was, incidentally, the first album purchased by Frank Zappa. Jack Skurnick, director of EMS Recordings, was the first to produce recordings of Varèse. This piece appears on the first Varèse recording, EMS 401: Complete Works of Edgar Varèse, Volume 1. Sidney Finkelstein wrote in the liner notes about the work:
[Ionisation] is built on a most sensitive handling and contrast of different kinds of percussive sounds. There are those indefinite in pitch, like the bass drum, snare drum, wood blocks, and cymbals; those of relatively definite musical pitch, such as the piano and chimes; those of continually moving pitch, like the sirens and 'lion's roar.' It is an example of 'spatial construction,' building up to a great complexity of interlocking 'planes' of rhythm and timbre, and then relaxing the tension with the slowing of rhythm, the entrance of the chimes, and the enlargement of the 'silences' between sounds. There are suggestions of the characteristic sounds of modern city life.
- Chou, Wen-Chung (April 1966). "Varèse: A Sketch of the Man and His Music". The Musical Quarterly LII (2): 151–170. doi:10.1093/mq/LII.2.151. Retrieved 2008-04-06.
- "Ionisation, for 13 percussionists". allmusic. Retrieved 30 August 2010.
- Radice, Mark A. (1989). ""Futurismo:" Its Origins, Context, Repertory, and Influence". The Musical Quarterly 73 (1): 1–17. doi:10.1093/mq/73.1.1. Retrieved 2008-04-06.
- Bernard, Jonathan W.; Van Solkema, Sherman (Autumn 1980). "Review of The New Worlds of Edgard Varèse: A Symposium (ed. Sherman Van Solkema, contributions by Elliott Carter, Chou Wen-Chung and Robert P. Morgan)". Journal of Music Theory 24 (2): 277–283. doi:10.2307/843507. JSTOR 843507.
- François, Jean-Charles; Francois, Jean-Charles (Winter 1991). "Organization of Scattered Timbral Qualities: A Look at Edgard Varèse's Ionisation". Perspectives of New Music 29 (1): 48–79. doi:10.2307/833066. JSTOR 833066.
- Wilheim, András (1977). "The Genesis of a Specific Twelve-Tone System in the Works of Varèse". Studia Musicologica Academiae Scientiarum Hungaricae. T. 19 (Fasc. 1/4): 203–226. doi:10.2307/901798. JSTOR 901798.
-  Stereophile magazine names the best recordings, including "EDGARD VARÈSE: The Varèse Record Ionisation, Density 21.5, Interpolations from Déserts, Octandre, Intégrales"
-  Article from Stereo Review by Frank Zappa about Ionisation.
- Video of performance