Sound of Silence
was first released on 19 October 1964 as a track on Simon & Garfunkel's Wednesday Morning, 3 A.M.
The album was a commercial flop. Seeing the track's potential, Columbia producer Tom Wilson took the previously recorded tape and overdubbed electric guitar and drums onto it. Columbia then re-released the new version of Sound of Silence
as a single in September 1965:
Paul Simon and Art Garfunkel knew nothing about Columbia's actions until they heard the new version of their song on the radio while in Europe. Paul Simon hated it immediately but it became their signature number and one of the top hit songs of all time.
A very different cover version by Disturbed was released on 7 December 2015:
It also went to #1 on the Billboard charts. Which version is better can be debated.