First-Ever Mixer and Crossfader Dates Back Over a Century

In 1910, the French engineer Leon Gaumant demonstrated his sound-and-film synchronizing Chronophone system at the Gaumant Palace—a 5,500 seat reconstruction of the Hippodrome, which was at the time Europe's largest movie theatre—in Paris, FR.

At the time, moving pictures with synchronized sound were limited in length by the playing time of a gramophone records—the longest was 200ft, at 16 frames-per-second.

Gaument's Chronophone had two gramophone platters, between which a deft operator could switch back and forth—a clever solution! More here.