Back in Argentina, Piazzolla formed his Orquesta de Cuerdas (String Orchestra), which performed with the singer Jorge Sobral, and his Octeto Buenos Aires in 1955. With two bandoneons (Piazzolla and Leopoldo Federico), two violins (Enrique Mario Francini and Hugo Baralis), double bass (Juan Vasallo), cello (José Bragato), piano (Atilio Stampone), and an electric guitar (Horacio Malvicino), his Octeto effectively broke the mould of the traditional orquesta típica and created a new sound akin to chamber music, without a singer and with jazz-like improvisations. This was to be a turning point in his career and a watershed in the history of tango. Piazzolla's new approach to the tango, "nuevo tango", made him a controversial figure in his native land both musically and politically. However, his music gained acceptance in Europe and North America, and his reworking of the tango was embraced by some liberal segments of Argentine society, who were pushing for political changes in parallel to his musical revolution.