Gregorian is a German band, headed by Frank Peterson, which reads, using the Gregorian chant, the most famous pop songs, rock and metal. Because their arrangements that include both sung instrumental accompaniment, it is not possible to label such as pure Gregorian chant (modulated on the exclusive use of the voice with the absence of any instrumentation).
Originally, Gregorian was conceived as a group more pop-orientated, building on the success of Enigma. So it was that in 1991 was born the album Sadisfaction, to the accompaniment of vocal duo The Sisters of Oz Susana Espelleta (Peterson's wife at the time) and Birgit Freud. However, this is the only album in that style.
In 1998, Peterson and his team decided to do covers of famous songs in the Gregorian style.