Listening to music is a common means of entertainment. The culture surrounding music extends into areas of academic study, journalism, philosophy, psychology, and therapy. The music industry includes songwriters, performers, sound engineers, producers, tour organizers, distributors of instruments, accessories, and publishers of sheet music and recordings. Technology facilitating the recording and reproduction of music has historically included sheet music, microphones, phonographs, and tape machines, with playback of digital musics being a common use for MP3 players, CD players, and smartphones.