Julián Carrillo Trujillo (January 28, 1875 – September 9, 1965) was a Mexican composer, conductor, violinist and music theorist, famous for developing a theory of microtonal music which he dubbed "The Thirteenth Sound" (Sonido 13). Biography Carrillo was born on January 28, 1875, in Ahualulco, a village in the state of San Luis Potosí. He was the last of the 19 children of Nabor Carrillo and Antonia Trujillo. Early education Carrillo sang in the children's choir of Ahualulco's church. The choir's conductor, Flavio F. Carlos, encouraged him to study music in the state capital, San Luis Potosí. He planned to study for two years, then return to Ahualulco as the church's singer, but problems prevented this plan. He arrived to San Luis Potosí City in 1885 and began to study with Flavio F. Carlos, teacher to several generations of San Luis Potosí's composers. Carrillo also began to work in his teacher's orchestra where he was a percussionist and later, violinist. He composed his first small works for this group. Because of his family's financial situation, Carrillo left his primary school studies early, but continued working in the orchestra and studying music with Carlos. In 1894, Carrillo composed a mass that was locally successful. This, along with a letter of recommendation from the government of San Luis Potosí, allowed him to go to study in the National Conservatory of Music in Mexico City. Carrillo made quick progress in the Conservatory. His professors included Pedro Manzano (violin), Melesio Morales (composition), and Francisco Ortega y Fonseca (physics, acoustics, and mathematics). Having not completed primary studies, he was ignorant of the acoustic basis of music—so he was fascinated when Ortega discussed laws governing generation of fundamental intervals in music. For example, when a violin string is depressed (stopped) at its midpoint, it produces a pitch twice the frequency of (an octave above) the open string. When a string is stopped at one-third, the remaining two-thirds vibrates a perfect fifth higher than the open string (almost exactly equivalent to 5/8 of an octave). Carrillo explored these relationships in experiments. For a while he tried, but couldn't divide the string further than into eight equal parts. Then he left the traditional way of dividing the string into two, three, four, five, six, seven and eight equal parts, and, using a razor to stop the string, divided the fourth string of his violin between G and A