Ska was a Jamaican dance music that swept out of Jamaica in the early 1960s to shake the butts of working- and middle-class Jamaicans before going on, via the West Indian immigrant connection, to the UK, and then on to the world. In the UK, ska was also known as blue beat music. Rocksteady, and later, reggae sprang from the loins of ska in the late 1960s. Mid-1970s and 1980s/1990s revivals of this popular dance form have kept thismusic alive and fun through the present. The ska beat on drums and bass, rhythm guitar, lots of horns and maybe a Farfisa or Hammond organ --- that's the ska sound.
For the musically inclined, here is a description of the rhythmic structure of ska:
Musically, Ska is a fusion of Jamaican mento rhythm with R&B, with the drum coming in on the 2nd and 4th beats, and the guitar emphasizing the up of the 2nd, 3rd, and 4th beats. The drum therefore is carrying the blues and swing beats of the American music, and the guitar expressing the mento sound. (taken from The Attempted SKA page)
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