Julián Carrillo Trujillo (January 28, 1875–September 9, 1965) was a Mexican microtonal composer and musical scientist. He devised Sonido 13 ("The Thirteenth Tone"), a microtonal music system for composition beyond the conventional western twelve-note octave. While experimenting with his violin in 1895, Julián Carrillo discovered the sixteenths of tone, i.e., sixteen clearly different sounds between the pitches of G and A emitted by the fourth violin string. Because there are six whole tones in conventional tuning to the next octave, a musical scale made with sixteenths of each tone has 96 different notes or pitches. In contrast to this, the scale made with half-tones has only 12 pitches. On the basis of this discovery, Carrillo proposed a radical change of the musical system. The "Thirteenth Sound" revolution is an attempt to incorporate musical microintervals into the musical system, i.e., to compose music with microintervals. The number 13 is not a proposal to use a scale made with thirteen sounds, but a symbol of the break with the traditional twelve-pitch (chromatic) scale that has been the basis of Western musical system. When a composer breaks with the twelve-pitch scale, he or she is in front of an infinity of tempered and non tempered scales for composition. Julián Carrillo reformed theories of music and physics of music. He invented a surprisingly easy musical notation based on numbers that can represent scales based on any musical interval within the octave, like thirds, fourths, quarters, fifths, sixths, sevenths, and so on (even if Carrillo wrote, most of the time, for quarters, eights, and sixteenths combined, the notation is able to represent any imaginable subdivision). He invented, adapted, and made new musical instruments that can produce microintervals. He composed a large amount of microtonal music and recorded about 30 of his compositions. Carrillo published his Theory of the Thirteenth Sound in the twenties years. It is therefore a contemporary of other microtonal musical proposals made by the Czech Alois Hába and the French-Russian Ivan Wyschnegradsky. They all began to compose music in quarter of tones in the twenties and had to adapt musical instruments to produce those microintervals. But Carrillo's proposal (the Thirteenth Sound) was deeper, more radical and more comprehensive. While European musicians discussed the possibility of composing with thirds or quarters of tone, and some of them did the first timid attempts of composing with these intervals, Carrillo demonstrated the possibility of writing for sixteenth of tones. The first conferences on, and demonstrations of, microtonal music occurred in 1924. Some early demonstrations were broadcast. In February the 15th, 1925, the first Thirteenth Sound concert was performed, in the Teatro Principal (Principal Theater) of Mexico City. On December of that year, the Thirteenth Sound was presented in Havana - and the following March in New York City. Julian Carrillo devoted his remaining life to consolidate his microtonal musical proposal, named "The Thirteenth Sound Revolution". He composed about a hundred works. He lectured about music and acoustics in America and Europe. He taught his theories in the Escuela Nacional de Música (UNAM) and privately. He conducted and organized a Thirteenth Sound Orchestra in which all instruments were able to produce microintervals. He made microtonal instruments and wrote many books. Some of his works are: Preludio a Colón (Prelude to Columbus for voice with chamber ensemble, 1922, first performed in 1924); Sonata casi fantasia for violin, violoncello and guitar in quarter-, eighth- and sixteenth-tones (1925); Concertino in quarter-, eighth- and sixteenth-tones for violin, cello and harp with orchestra (1926, commissioned by Leopold Stokowski who also commissioned the first of two Columbus Symphonies in quarter-, eighth- and sixteenth-tones, both 1926); Horizons: Symphonic Poem for violin and cello in quarter- and eighth-tones and harp in sixteenth-tones with orchestra (1947); two Concertos for violin and orchestra in quarter-tones (1949 and 1959); and Mass to Pope John XXIII for male voices acapella in quarter-tones ("Mass of Restoration", 1962). Among the new instruments he made are fifteen "metamorphoser" pianos which produce scales from whole tones to sixteenths.