 Rock groups also began using synthesizers and electronic keyboards alongside the traditional line-up of guitar, bass and drums; particularly in progressive rock groups such as Genesis, Emerson, Lake & Palmer and Pink Floyd.The pop-blues-rock band Fleetwood Mac was also known for synthesizer-infused hits during this period.Keyboardists are often hired in cover bands and tribute bands, to replicate the original keyboard parts and other instrumental parts such as strings or horn section where it would be logistically difficult or too expensive to hire people to play the actual instruments.