Low-fidelity magnetic wire recorders had been in use since around 1900[18] and in the early 1930s the movie industry began to convert to the new optical sound-on-film recording systems based on the photoelectric cell.[19] It was around this time that the German electronics company AEG developed the first practical audio tape recorder, the "Magnetophon" K-1, which was unveiled at the Berlin Radio Show in August 1935