4 Walls by f(x)

4 Walls is the fourth studio album by South Korea-based girl group f(x), released by S.M. Entertainment on October 27, 2015. Lee Soo-man, former president of S.M. Entertainment, served as the executive producer of the album. It marked the group's first release as a four-member group after former member Sulli left the group in August 2015. To promote the album, f(x) appeared and performed on several music programs including M Countdown, Music Bank and Show! Music Core. The group further embarked on its first concert tour Dimension 4 – Docking Station (2016), which visited South Korea and Japan in January and February 2016. The title track "4 Walls" was released as a single in conjunction with the release of the album. The record's musical styles are diverse, incorporating the group's signature electropop and synthpop sound with elements of various genres including house, EDM and UK garage. The album received favorable reviews from music critics, who noted that the other members had the opportunity to showcase their vocal abilities more following the departure of Sulli. The release peaked atop South Korea's Gaon Album Chart and has sold over 76,000 physical copies in the country as of January 2016; in addition, 4 Walls topped the Billboard World Albums Chart and charted at number thirty-nine on the Japanese Oricon Albums Chart. The single "4 Walls", meanwhile, peaked at number two on the Gaon Digital Chart and the Billboard World Digital Songs.