The pallophotophone (also known as the RCA Photophone) was an audio recording device developed by General Electric researcher Charles Hoxie ca. 1922. Hoxie took the name of the device from the Greek words for "shaking light sound".
The pallophotophone was a optical sound system which could record and replay multiple audio tracks on unsprocketed 35mm Kodak monochrome film using a photoelectric process that captured audio wave forms generated by a vibrating mirror. It is thought to be the world's first effective multitrack recording system, predating magnetic tape multitrack recording by at least 20 years.
GE experimented with the system by recording many early radio broadcasts from its Schenectady, New York radio station WGY in the 1920s and early 1930s. In the mid-1920s GE developed a variable-area sound-on-film motion-picture sound system based on Hoxie's work which was subsequently marketed as a commercial product by RCA (then a GE subsidiary) as RCA Photophone. Western Electric would later take over the Photophone trademark.
It is believed that none of the original pallophotophone machines built by GE have survived to the present day, although a few reels of pallophotophone recordings of radio broadcasts still exist. In 2008, thirteen reels were rediscovered in the archives of the Schenectady Museum by curator Chris Hunter and John Schneiter, a former GE researcher and board member at the museum. The film was labeled "radio programs of 1929-1930” and had many unique features that differentiated them from early movie films. Schneiter then contacted his former colleague, Russ DeMuth, a mechanical engineer at GE Global Research to help decipher the mysterious film. Unlike movie film, the discovered reels did not contain sprockets. Hunter, Schneiter and DeMuth studied the original patents and photographs of the original pallophotophone and built a new player from scratch using modern components that was able to recover the audio from the reels.
Among the material on the surviving reels is the earliest known recording of the NBC chimes, a broadcast of a high school basketball match (believed to be the world's second-oldest recording of a sports broadcast) and a historic 1929 recording of the 82-year-old Thomas Edison, with Henry Ford and President Herbert Hoover, speaking on a broadcast commemorating the 50th anniversary of the invention of the incandescent light bulb.
- Interview with Russ DeMuth, "Reinventing the Pallophotophone", 'Edison's Desk' blog
- James Grahame, "Recreating The RCA Photophone", Retro Thing website
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