The Mellotron is a pre-digital keyboard instrument that is considered the ancestor of the modern sampler. Inside the machine is a bank of magnetic audio tapes. When a key is pressed, a playback head moves against a specific strip of tape, playing a 7-second recording of a real instrument—most commonly violins, cellos, or choirs. When the key is released, a spring pulls the tape back to the start. Because it used actual recordings, it provided a level of realism that synthesizers of the time could not achieve, though it was notoriously temperamental and heavy. Its most famous appearance is the 'flute' introduction to The Beatles' 'Strawberry Fields Forever.' Progressive rock bands like King Crimson and Genesis used it extensively to create orchestral soundscapes on tour without needing a real orchestra. It defined the 'psychedelic' and 'symphonic rock' sounds of the late 1960s and 70s.