From Wikipedia:
“The Sounds of Silence” is the song that propelled the 1960s folk music duo Simon and Garfunkel to popularity. It was written by Paul Simon in the aftermath of the assassination of President John F. Kennedy on November 22, 1963. Simon conceived of the song as a way of capturing the emotional trauma felt by many Americans left by the sudden death of a vigorous and visionary leader. It was originally recorded as an acoustic piece for their first album Wednesday Morning, 3 A.M. but was later overdubbed with electric instruments and released as a single. The single slowly climbed the charts until it reached number one on New Year’s Day 1966. The song was included in the 1966 album Sounds of Silence.
The song features Simon on acoustic guitar and both Simon and Garfunkel singing.
The song was originally called “The Sounds of Silence”, and is titled that way on the early albums in which it appeared and on the single. In later compilations, it was retitled “The Sound of Silence”. Both the singular and the plural form of the word appear in the lyrics.