In 1923, the Phonofilm, the first motion picture with a sound-on-film track was demonstrated at a press conference. It was developed (1920) by Dr. Lee De Forest, inventor of the radio tube (1907). Dancers and musicians were shown on the film with music, but without voice dialogue. The sound was imaged in a narrow margin alongside the picture frames on the film. (De Forest's process came several years before the 1928 film, the "Jazz Singer," but that film used the Warner Vitaphone system. The Vitaphone system attempted to synchronize its sound from a record player turntable connected to the film projector.) The de Forest process read a series of light and dark areas on the film itself, using a photocell to convert to audio.