Music without sound

Sofia Gubaidulina
Silence in music happens when the music stops during a performance. It is sometimes replaced by gesture music. In his Sofia Gubaidulina biography,[2] Michael Kurtz mentions the silent solo performance by the conductor included in ...Stimmenn... verstummen..., an orchestral work from 1986.

The symphony is notable for its careful and innovative use of silence. Though the eighth movement has the largest proportions of the work, the climax actually takes place in the ninth movement when the conductor motions before a silent orchestra. The motions the conductor makes are meant to make his hands move increasingly farther apart from each other according to the Fibonacci sequence. This "conductor solo" is repeated at the end of the work, when after the last note is sounded the conductor continues to motion for several minutes.
From Wikipedia ...Stimmenn... verstummen... article

Milan Knizak
From 1960, the International Fluxus Movement created a number of Events or Verbal Pieces, whose temporal structures were typically vague so as to be sometimes without beginning nor end, with or without sound, with or without music. A remarkable example is that of Czech artist Milan Knizak's 1965 Snowstorm N°1 whose score states: Paper gliders are distributed to an idle and waiting audience.

Another Event, by Czech Fluxus artist Milan Knizak, is called Snowstorm N°1 (1965) and simply instructs that "Paper gliders are distributed to an idle and waiting audience". What results is a snowstorm of quietly gliding paper airplanes as the audience returns them back and forth and so on. The exchange of sheets is experimentaly beautiful, like the caring gesture toward the instrument as tended by Brecht.
[From Not the Other Avant-garde].[3]

Helmut Lachenmann
Lachenmann composed Salut Für Caldwell for 2 guitars in 1977. The piece includes silent moments when "the players silent motions and gestures created a space of unheard music ". [Michael Kurtz[4]]

Takehisa Kosugi
In 1963 Takehisa Kosugi composed for Fluxus 1 a musical piece called Theatre Music in the form of a rectangle of cardstock that bore the trace of a spiral of moving feet. This was paired with the instructions: "Keep walking intently".[5]

Juan María Solare

• His work Gestenstücke (2008) is a collection of five pieces for 4 performers in which a musical structure is used to put order in non-sounding elements, concretely gestures. For instance, the first piece of the cycle is a canon of gestures. Premiere: University Bremen, Ensemble Neues Musiktheater, June 12, 2008.
• Another non-sounding piece is his conceptual work called Tense Atmosphere a graphic score which consists of a silence with a sforzato sign (2013).

Maximilian Stadler (1748-1833)

A sequence of finite instructions, an algorithm relates to computation, which ultimately relates to music. Eighteenth century algorithmic music is a contemporary of automaton machines, like Jacques de Vaucanson's duck or Wolfgang von Kempelen's chess player, or Ada Lovelace and Charles Babbage's 1822 difference engine. In 1787, W.A. Mozart (1756–1791) devised an aleatoric system called Musikalisches Würfelspiel (Musical Dice) published 1793, to compose waltzes with a pair of dice and a set of written bars on paper cards.[6] The combination of all the 16 cards and transitions, of which there are theoretically ${\displaystyle 10^{29}}$ combinations, constitutes a minuet.[7]

Austrian composer Maximilian Johann Karl Dominik Stadler, also known as Maximilian Stadler (1748–1833), created a table to compose minuets and trios with a pair of dice. In the case of the minuet version, there are 16 cards with one bar each and preconceived transitions between certain musical measures. Mathematical games columnist Martin Gardner once remarked in an article about automated music composition. "If you fail to preserve it, it will be a waltz that will probably never be heard again."[8]

The method of pure aleatoric music was used in the twentieth century by US composer Lejaren Hiller.

Wladimir Baranoff-Rossiné[9] started building his optophonic piano in the 1915s. A set of painted glass discs are rotated via the small keyboard. Light is projected through the discs onto the wall. The player can control intensity of light and speed of rotation. 6 or 8 keys of the 3-octaves keyboard are devoted to colored discs. It is not clear what kind of sound the keyboard is able to produce. Oscillator frequencies (as stated in some articles) are rather unlikely between 1915-1920. More probably the light show was performed with piano accompaniment, maybe performed on the reduced keyboard of the Optosonic Piano, akin to a toy piano.

At one point, the music exists in the composer's mind. In 1928, Edgard Varèse started working on an opera called L'Astronome based on North American Indian legends, a project he never completed and destroyed the drafts. In 1932, he asked Antonin Artaud to write the libretto of a large scale oratorio, Il n'ya plus de firmament (There is no longer any firmament). In his book Phantasmatic Radio Allen S. Weiss translates the beginning of Artaud's text:

Darkness. Explosions in this darkness. Harmonies suddenly broken off. Harsh sounds. Depressurized soundings. The music will give the impression of a distant cataclysm and will fill the room, falling as from vertiginous heights. Chords will originate in the sky and then deteriorate, going from one extreme to the other. Sounds will fall as if from very high, then suddenly stop and spread out in bursts, forming vaults and parasols. Tiers of sounds... [in Phantasmatic Radio][10]

The piece was never completed and Varèse turned to other projects, including a radiophonic work involving various synchronised choirs located in different places of the world. He never found the technology for it. In 1948, Artaud insisted on having noise sounds included in his Pour en finir avec le judgement de Dieu (To have done with the judgment of God). This was done in the Radiodiffusion Television Française studios where Pierre Schaeffer was working at the time.

Silent Music (1994)[11] is an installation work by Canadian artist Robin Minard (b1953) with several hundred wall-mounted piezo loudspeakers and four-channel audio. The miniature loudspeakers are displayed in plant-like shapes on the walls of public spaces. They reproduce the minuscule ambient sounds of the public space where they are installed or play random synthetic sounds at barely audible volume. Minard deals with remote sounds best suited to intimate listening. In 2006 he created 'A voir en silence', a small artist book with loudspeakers and hand-written text.[12]

Marcel Proust
The Vinteuil Sonata is an imaginary violin and piano sonata by fictitious composer Vinteuil recurring several times in Marcel Proust's À la recherche du temps perdu (In Search of Lost Time), particularly in Un amour de Swann (1913). In the latter volume, Charles Swann associates strong emotions and memories to the melody composed by Vinteuil. The French composer Reynaldo Hahn noticed how much Marcel Proust "vivait la musique de son temps" (experienced contemporary music).[13] For example, Proust immediately praised and enjoyed Debussy's 1902 Pelléas et Mélisande opera. Critics disagree on which composer inspired the sonata. Possibly Gabriel Fauré[14] or César Franck. In Les plaisirs et les jours (1896), Proust focusses on Hans Sachs's monologue from Wagner's Die Meistersinger von Nürnberg, act 2. In Jean Santeuil (1952), a Camille Saint-Saëns sonata for violin and piano (Op. 75, 1885) plays a key role and is presumably the model for the Sonate de Vinteuil. In Un amour de Swann, the Vinteuil Sonata is played during evenings at the Verdurins' by pianist Dechambre. The main character's emotions are mirrored by Proust's musical reminiscences.

Walter Marchetti
A good example of imaginary music can be found in a Walter Marchetti poem where he mentions a Juan Hidalgo imaginary composition (both Hidalgo and Marchetti were members of the Spanish Zaj Group of Madrid in the late 1950s). <poem style="margin-left: 2em;">Eat an iced popsicle and thus perform his free transcription, for only one performer, of Music For Five Dogs, an iced Popsicle and Six Male Performers by Juan Hidalgo. —Walter Marchetti in A Zaj Sampler[15]

• 4′33″: John Cage's silent composition - four minutes thirty-three seconds of silence
• List of silent musical compositions