House music grew out of the post-disco dance club culture of the early '80s. After disco became popular, certain urban DJs -- particularly those in gay communities -- altered the music to make it less pop-oriented. The beat became more mechanical and the bass grooves became deeper, while elements of electronic synth pop, Latin soul, dub reggae, rap, and jazz were grafted over the music's insistent, unvarying four-four beat. Frequently, the music was purely instrumental and when there were vocalists, they were faceless female divas that often sang wordless melodies. By the late '80s, house had broken out of underground clubs in cities like Chicago, New York, and London, and had begun making inroads on the pop charts, particularly in England and Europe but later in America under the guise of artists like C+C Music Factory and Madonna. At the same time, house was breaking into the pop charts; it fragmented into a number of subgenres, including hip-house, ambient house, and most significantly, acid house (a subgenre of house with the instantly recognizable squelch of Roland's TB-303 bass-line generator). During the '90s, house ceased to be cutting-edge music, yet it remained popular in clubs throughout Europe and America. At the end of the decade, a new wave of progressive house artists including Daft Punk, Basement Jaxx, and House of 909 brought the music back to critical quarters with praised full-length works.