With the composition of "Adiós Nonino" in 1959, Piazzolla established a standard structural pattern for his compositions, involving a formal pattern of fast-slow-fast-slow-coda, with the fast sections emphasizing gritty tango rhythms and harsh, angular melodic figures and the slower sections usually making use of the string instrument in the group and/or Piazzolla's own bandoneon as lyrical soloists. The piano tends to be used throughout as a percussive rhythmic backbone, while the electric guitar either joins in this role or spins filigree improvisations; the double bass parts are usually of little interest, but provide an indispensable rugged thickness to the sound of the ensemble. The quintet of bandoneon, violin, piano, electric guitar and double bass was Piazzolla's preferred setup on two extended occasions during his career, and most critics consider it to be the most successful instrumentation for his works. This is due partly to its great efficiency in terms of sound – it covers or imitates most sections of a symphony orchestra, including the percussion, which is improvised by all players on the bodies of their instruments – and the strong expressive identity it permits each individual musician. With a style that is both rugged and intricate, such a setup augments the compositions' inherent characteristics.