 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.