Edison Records
Thomas A. Edison invented the phonograph, the first device for recording and playing back sound, in 1877. After patenting the invention and benefiting from the publicity and acclaim it received, Edison and his laboratory turned their attention to the commercial development of electric lighting, playing no further role in the development of the phonograph for nearly a decade. Edison's original phonograph recorded on sheets of tinfoil and was little more than a crude curiosity, although one that fascinated much of the public. These earliest phonographs were sold mainly to entrepreneurs who made a living out of traveling around the country giving "educational" lectures in hired halls or otherwise demonstrating the device to audiences for a fee. The tinfoil phonograph was not fit for any real practical use and public interest soon waned.
Optical sound
After the war, Theodore Case and Earl I. Sponable collaborated with fellow wireless communications pioneer Lee de Forest, inventor of the Audion tube, to apply their optical sound system to motion pictures. De Forest had been granted general patents for a sound-on-film process in 1919, though it was the Case Research Lab's inventions which made de Forest's systems workable. Case Lab first converted an old silent-film projector into a recording device in 1922, using the projector's light for exposing a soundtrack onto film. The process (which de Forest called Phonofilm) recorded sound as parallel lines of variable shades of gray, photographically transcribing the electrical waveforms from a microphone, which were translated back into sound waves when the movie was projected.