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 a sound-on-film, "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 Brothers 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.
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Historically, the name Photophone had been first used for the telephony by light-beam invention patented by Alexander Graham Bell's Volta Laboratory in 1880.
A new, completely separate patent for sound-on-film technology was awarded to General Electric (GE) in 1925, which dubbed the process Photophone, a name that had been used in previous decades for other sound film processes. RCA, a GE subsidiary, took over the GE patent as part of a corporate competition with AT&T and their affiliate Western Electric, the primary sponsors of both the Vitaphone and Movietone systems.
Primary RCA (Photophone) licensees include:
Secondary RCA licensees include:
Primary Western Electric (Westrex) licensees include:
Secondary Western Electric licensees include:
Although variable-area sound recording is usually associated with RCA and variable-density sound recording is usually associated with Western Electric, these relationships are not cast into stone.
Both variable-area and variable-density systems were marketed by both RCA and Western Electric, with roughly equal measured and perceived quality from both systems, from both suppliers.
Neither system nor supplier was clearly superior to the other, except where individual laboratory processes made one system more consistently superior to the other.
Variable-density was preferred for Technicolor prints as this process utilized a silver "key" record, thereby creating a CMYK color image, and the sound track was also a silver record. The "key" record was deleted from most Technicolor prints after 1944, thereby creating a CMY color image, but Technicolor's strong preference for variable-density continued long thereafter.
Variable-density was finally abandoned as customer preferences for "dual-bilateral variable-area" sound tracks emerged in the late-1950s. This required changes to some laboratory processing and quality controls, but the real reason for variable-density's demise was yet to come.
In the mid-1970s, Westrex Corp. (a wholly owned subsidiary of Litton Industries since 1956, and the successor to Western Electric's cinema sound business unit) re-introduced the ca. 1938 "four ribbon" light valve, and the ca. 1947 RA-1231 sound recorder.
As the RA-1231 was actually a stereo variable-area recorder—although when it was originally introduced in 1947 it was a mono 35mm variable-density or variable-area recorder, or a 16mm variable-density or variable-area recorder, at the customer's option—variable-density's fate was sealed as stereo optical sound prints (as contrasted with stereo magnetic sound prints) became a marketing imperative.
When combined with Dolby Laboratories's encoding technology, the discrete L and R channels of Westrex's stereo variable-area system was renamed "Left Total" and "Right Total", and when decoded these produced the L, C, R and S sound image first popularized by Fox's CinemaScope system in 1953.
Stereo optical sound prints are compatible with all aspect ratios whereas stereo magnetic sound prints are only compatible with CinemaScope or CinemaScope-compatible wide screen processes. Stereo variable-area, therefore, provided for the first time a stereo sound system which was compatible with the industry standard non-anamorphic (i.e., spherical) "flat wide screen" (1.85:1) format and the industry standard anamorphic (2.35:1) format.
Nearly all original track negatives (OTNs) are now produced as stereo variable-area, and the former Western Electric (Westrex) system has been renamed Photophone and has become the de-facto standard, world-wide.
The RCA system was abandoned as it was incapable of producing time-aligned stereo OTNs, whereas time-aligned stereo OTNs were inherently a part of the Western Electric (Westrex) system since 1938.
The Westrex system was renamed Photophone after the Western Electric and Westrex registered trademarks were sold by AT&T and Litton, respectively, to others, for uses other than cinema sound systems.
Renaming the Westrex system to Photophone was facilitated by the demise of RCA's cinema sound business unit, by the hand of GE, RCA's acquirer, and by its failure to protect the Photophone trademark.
The Westrex system, renamed Photophone, is still in new production, with more than 100 systems currently in active service, world-wide. Some users, including Disney and Warner, have multiple systems. The RCA system is essentially defunct.
The (Westrex) Photophone system also has the capability of producing a DTS time-code track along with its native stereo variable-area tracks, or DTS time-code alone for use with 70mm and "special venue" prints.