In rock and pop, rhythm sections range in size from the barest, stripped-down size of the "power trio" (guitarist, bassist, and drummer) and the organ trio (Hammond organist, drummer, and a third instrument) to large rhythm sections with several stringed instrument players (mandolin, acoustic guitar, electric guitar, etc.), multiple keyboard players (e.g., piano, Hammond organ, electric piano, synth), two instruments playing a bass role (e.g., bass guitar and synth bass) and a group of auxiliary percussionists (congas, shakers, etc.) to fill out (or "sweeten") the sound. Some rhythm sections combine electronic/digital instruments that are sequenced, pre-recorded backup tracks and live instruments (including electric, electronic and acoustic instruments).