RCA Photophone was the trade name given to one of four major competing technologies that emerged in the American film industry in the late 1920s for synchronizing electrically recorded audio to a motion picture image. RCA Photophone was an optical sound, "variable-area" film exposure system, in which the modulated area (width) corresponded to the waveform of the audio signal. The three other major technologies were the Warner Bros. Vitaphone sound-on-disc system, as well as two "variable-density" sound-on-film systems, Lee De Forest's Phonofilm, and Fox-Case's Movietone.
When Joseph P. Kennedy and other investors merged Film Booking Offices of America (FBO) with the Keith-Albee-Orpheum theater chain and Radio Corporation of America, the resulting movie studio RKO Radio Pictures used RCA Photophone as their primary sound system. In May 1929, RKO released Syncopation, the first film made in RCA Photophone.