An electric guitar is a guitar using pickups to convert its metal string vibration into electricity. This is amplified with an instrument amplifier. The output is altered with guitar effects such as reverb or distortion. The earliest electric guitars were hollow bodied acoustic instruments with tungsten steel pickups made by Rickenbacker in 1931. The electric guitar was a key instrument in the development of musical styles that emerged since the late 1940s, such as Chicago blues, early rock and roll and rockabilly, and 1960s blues rock. It is used in almost every popular music genre.