"Achtung Baby" is certified 8× platinum in the US by the RIAA, and according to Nielsen Soundscan, the album had sold 5.5 million copies in the country by March 2009. The record has been certified 5× platinum in Australia, 4× platinum in the UK, and diamond in Canada, the highest certification award. Overall, 18 million copies have been sold worldwide. It is U2's second-highest-selling record after "The Joshua Tree", which has sold 25 million copies. For the band, "Achtung Baby" was a watershed that secured their creative future, and its success led to the group's continued musical experimentation during the 1990s. "Zooropa", released in 1993, was a further departure for the band, incorporating additional dance music influences and electronic effects into their sound. In 1995, U2 and Brian Eno collaborated on the experimental/ambient album "Original Soundtracks 1" under the pseudonym "Passengers". For "Pop" in 1997, the group's experiences with dance club culture and their usage of tape loops, programming, rhythm sequencing, and sampling resulted in their most dance-oriented album.