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A rhythm section is the group of musicians in a rock music, jazz, or country music group who play their instruments to set out the pulse or beat of the music. This is played in accompaniment to the rest of the band. Some of the rhythm section instruments, such as the guitar and the piano, also play the chord progression (sequence of chords) that a song is based upon. Some rhythm section instruments, such as the drums and percussion, are just used to set out the beat. Most rhythm sections include a bass instrument, such as the bass guitar or the double bass, which plays the deep, low notes of the chord progression.