In 1970, the television show "Soul Train" premiered featuring famous soul artists who would play or lipsync their hits while the audience danced along. By the mid-1970s, disco had become one of the main genres featured. In 1974, "Billboard" added a Disco Action chart of top hits to its other charts (see List of "Billboard" number one dance club songs). Disco was characterized by the use of real orchestral instruments, such as strings, which had largely been abandoned during the 1950s because of rock music. In contrast to the 1920s, however, the use of live orchestras in night clubs was extremely rare due to its expense. The disco craze reached its peak in the late 1970s when the word "disco" became synonymous with "dance music" and nightclubs were referred to as "discos".