This vinyl record represents one of the most significant documents of Cuban revolutionary musical experimentation. The Grupo de Experimentación Sonora (Sound Experimentation Group) was founded at ICAIC (Instituto Cubano del Arte e Industria Cinematográficos) to create innovative soundtracks for Cuban cinema, becoming an incubator for what would emerge as the Nueva Trova movement that defined revolutionary Cuban music.
The cover design by Paola delivers powerful visual impact through stark contrast and provocative imagery. A skeletal or emaciated figure raises a revolver overhead in a gesture of defiance, rendered in expressive purple brushwork against a vibrant yellow background. The enormous "33" dominating the composition references the record's 33 RPM speed while suggesting revolutionary dates or numerical symbolism. Purple and yellow frames create bold geometric structure, while the Nueva Trova publishing logo appears in the corner. This raw, confrontational aesthetic captures the experimental and politically charged atmosphere of late 1960s Cuban culture.
Under the general and musical direction of composer Leo Brouwer (with co-directors Juan Márquez and Armando Guerra), this ensemble brought together musicians who would become legendary figures in Cuban music: Pablo Milanés, Silvio Rodríguez, Noel Nicola, Sara González, Sergio Vitier, and Eduardo Ramos. The group members played multiple instruments and composed collaboratively, creating a laboratory for musical innovation.
The recording includes striking experimental pieces: "Eramos" with text by José Martí and music by Pablo Milanés, "Salgo de Casa" by Eduardo Ramos, "El Bala" by Pablo Milanés, "Sondeando" by Eduardo Ramos, "El Viejo Obrero" by Silvio Rodríguez, and "Canción del Constructor" by Pablo Milanés. Additional collaborators included Amado del Rosario on electric oboe and various wind and brass instrumentalists. Recorded at ICAIC studios with design by Pablo Labañino and production by Pablo Menéndez, this album was produced and distributed by EGREM (Empresa de Grabaciones y Ediciones Musicales) on their Areito label, catalog number LD-3460.