Sonido 13 is a theory of microtonal music created by the Mexican composer Julián Carrillo around 1900 and described by Nicolas Slonimsky as, "the field of sounds smaller than the twelve semitones of the tempered scale". Developed in 1895 while he was experimenting with his violin. As Carrillo was placing his finger over a violin string, he noticed that he could produce different sounds than the ones defined by musical convention. This way, he realized that the string could be divided into an infinite number of pitches, creating many more possibilities for music composition. Though he became internationally recognized for his system of notation, it was never widely applied. His first composition in demonstration of his theories was Preludio a Colón (1922).
The Western musical convention up to this day divides an octave into twelve different pitches that can be arranged or tempered in different intervals. Carrillo termed his new system Sonido 13, which is Spanish for "Thirteenth Sound" or Sound 13, because it enabled musicians to go beyond the twelve notes that comprise an octave in conventional Western music.
« El Sonido 13 será el principio del fin y el punto de partida de una nueva generación musical que llegue a transformarlo todo. »
« The Thirteenth Sound will be the beginning of the end and the starting point of a new musical generation coming to transform everything. »
(Julián Carrillo )
Early life 
Julián Carrillo was a native of the state of San Luis Potosí in Mexico. He attended the National Conservatory of Music in Mexico City, where he studied Violin, Composition, Physics, Acoustics, and Mathematics. The laws that define music intervals instantly amazed Carrillo, which led him to conduct experiments on his violin. He began analyzing the way the pitch of a string changed depending on the finger position, concluding that there had to be a way to split the string into an infinite number of parts. One day, Carrillo was able to divide the fourth string of his violin with a razor into 16 parts in the interval between the notes G and A, thus creating 16 unique sounds. This event was the beginning of Sonido 13 that led Carrillo to study more about physics and the nature of intervals.
Professional life 
Carrillo became an excellent musician at the Conservatory and received a scholarship to study in Leipzig Royal Conservatory. After Carrillo returned to Mexico in 1918, he became conductor of the National Symphony Orchestra and in 1920 he also became Principal of the National Conservatory of Music. It was during this time that he began to invest a significant amount of time on Sonido 13. His achievements in this area were extensive and consisted of writing over 20 books, making more than 40 compositions, patenting fifteen pianos capable of producing small intervals, and organizing the Sonido 13 Symphonic Orchestra that performed in different parts of the world, playing microtonal music composed by Carrillo in different intervals. In 1933, Ahualulco, the town where Julián Carrillo was born, was renamed to Ahualulco del Sonido 13 in honor of Carrillo's work.
Music theory 
Julián Carrillo was a pioneer of microtonal music in the Western world. Julián Carrillo started dividing whole tones (major seconds) into 16 intervals, but he did not stop there. Through experiments, Carrillo noticed that he could divide the string into an infinite number of intervals, or into as many intervals as it is physically possible. Carrillo created intervals of 3 ( Play (help·info)), 4 ( Play (help·info)), 5 ( Play (help·info)), 16 ( Play (help·info)), 32 ( Play (help·info)), 64 ( Play (help·info)), and 128 ( Play (help·info)) tones within a major second, leaving the formula to create more, if desired. However, as the number of intervals increases it becomes harder to distinguish the notes from each other (see just noticeable difference).
Music notation 
Because new sets of sounds were created, it was imperative to make a new notation system. Carrillo developed an easy method for notation, which would help people not familiar with previous forms of notation to quickly learn to read and write music.
To show how easy the new writing system was, Carrillo gave two New York elementary school boys, who had no prior knowledge of Sonido 13, a simple work by Bach to convert to his notation system. The boys accomplished the task in less than an hour, proving that the new writing method was easy to learn.
The new writing system is not as graphic as the conventional staff or stave, and instead of calling the notes by a letter or a syllable (Do, Re, Mi, etc.) they are represented by a number. The numbering system starts with a zero and increments by one until the last note of the octave is reached. Within this system, the number of notes in an octave is dependent on the number of intervals that one wishes to create within a whole tone.
Carrillo used many intervals, although mainly in multiples of 4 such as 16, 32, and 64 so that between each of the whole tones, 16, 32, or 64 additional notes were created. Carrillo called these intervals 16hs of a tone, 32nds of a tone, and 64ths of a tone, respectively. As a result, C would be labeled 0, D flat would be labeled 8, D would be labeled 16, E flat would be labeled 24, E would be labeled 32, etc., for 16ths of a tone.
When notating music, Carrillo used a staff. However, instead of using lines to signify different notes, he used the lines to distinguish between octaves so that each line on the staff represents a different octave. For example, if 0 on the second line of the staff denoted what conventional music terms middle C, 0 on the third line would refer to C an octave higher, and 0 on the first line would refer to C an octave lower.
Musical instruments 
This system added sounds unexplored by generations of musicians, so new adaptations of current instruments had to be made to support the small intervals, and for this reason the instruments were reduced in the number of octaves they contained. For example, a standard piano has 88 keys that cover more than 7 so-called octaves, and a piano with 88 keys made for 16ths of a tone would not constitute a full so-called octave. To have the same number of so-called octaves as a conventional piano, a piano for 16ths of a tone would need 704 keys. So, using logic and innovative thoughts of modern luthiers, a traditional piano will be enriched infinitely. Every existing instrument has to be modified to adapt to the new rules of the Sonido 13 system, but also new instruments have to be designed and created. Thus, modern luthiers have an almost fantastic but still unexplored world in front of them, except by Carrillo's mind.
Latest news 
New efforts are being done to resurrect the 13th Sound music and theory. In 2005 Mexican cellist Jimena Gimenez recently recorded the entire Carrillo's Cello Sonatas and Mexican-Quebecer guitarist Angélos Quetzalcóatl (The "Ambassador" of the 13th Sound) recorded almost all the guitar repertoire.
Besides these recording efforts, new music is being created using the Sonido 13 teachings and the Official Julián Carrillo Website was created by 13th sound musicians Armando Nava and Hugo Vargas. The website soon became extremely popular among Sonido 13 researchers and it gained the "Official" Status in 2009 thanks to the decision of Angel and Miguel Carrillo, executors of the Julián Carrillo Estate.
The "Ambassador of the 13th Sound" travels around the world promoting the 13th Sound principles which are: 1.- To Purify Music. 2.- To Enrich Music. 3.- To Facilitate Music. He has achieved international recognition by Government Institutions, the executors of the Carrillo Estate and his peers due to his formidable commitment for totally resurrecting the Revolution of the 13th Sound.
Further reading 
- Carrillo, Julián (1930). Rectificación Básica al Sistema Musical Clásico (2nd Edition). Editorial del Sonido 13. (Spanish)
- Carrillo, Julián (1945). 3 Conferencias (3rd Edition). Editorial del Sonido 13. (Spanish)
- Carrillo, Julián (1948). Sonido 13. Editorial del Sonido 13. (Spanish)
- Carrillo, Julián (1957). El Infinito en las Escalas y en los Acordes. Editorial del Sonido 13. (Spanish)
- Winkler, Ernesto S. (2006-06-07). "Julián Carrillo y el Sonido 13: Un Sistema Microtonal/Julian Carrillo and the 13th Sound: a microtonal musical system.". Retrieved 2006-09-20. (Spanish)/(English)
- Mena, María Cristina (1914). "Julian Carrillo: The Herald of a Musical Monroe Doctrine", The Century illustrated monthly magazine, Volume 89. Josiah Gilbert Holland and Richard Watson Gilder, eds. Digitized 2008.
- Randel, Don Michael, ed. (1996). "Carrillo (Trujillo), Julián (Antonio)", The Harvard Biographical Dictionary of Music, p.138. ISBN 0-674-37299-9.
- Slonimsky, Nicolas (1945). Music of Latin America, p.229. 1972 ISBN 9780306711886. Cited in Bethell (1998), p.95.
- Malmström, Dan (1974). Introduction to Twentieth Century Mexican Music, p.34-36. ISBN 91-7222-050-3.
- Bethell, Leslie, ed. (1998). A Cultural History of Latin America: Literature, Music and the Visual Arts in the 19th and 20th Centuries, p.95. ISBN 0-521-62626-9.
- Sonido13.com. (Spanish)
- "Sonido 13 & Julian Carrilo" (in Spanish). 2006-05-29. Retrieved 2006-09-20.