in North America, RCA and Western Electric (Northern Electric, in Canada), which licensed their principal sound element (original track negative) recording systems on a non-exclusive basis. In general, motion picture producers elected to license one or the other. In a few cases, where mergers had occurred, a producer might be licensed for both. For many years, it was customary to "brand" a film with its sound system, variously as "RCA Sound Recording", "Western Electric Recording", or similar brands, often including the corporate logo of the licensor (Meatball for RCA; The Voice of Action for Western Electric; Li Westrex for the post-1956 divestiture of Western Electric under Litton Industries' ownership). Such branding ceased in about 1976, particularly after nearly all optical sound recording (for release prints) had been converted to Westrex's stereo variable-area system from RCA's and Westrex's mono systems, although there were a few examples of such branding thereafter (mainly Westrex.) Many years later, the Photophone trademark would be reused by the Western Electric/Westrex stereo variable-area system, after both the Western Electric and Westrex trademarks became unavailable due to corporate asset sales by the disintegrating Bell System, but the Western Electric/Westrex stereo variable-area system continued to be marketed by a successor, and it is still serviced and supported to this day, although it is no longer branded as Photophone. Comparison of (mono) variable-area and variable-density Although variable-density sound system recording is usually associated with Western Electric and variable-area sound system recording is usually associated with RCA, these relationships are not cast into stone. Both variable-area systems and variable-density systems were marketed by both RCA and Western Electric, the Western Electric light valve being capable of producing either variable-density or variable-area depending on which ribbon axis was parallel to the film motion, and the RCA galvanometer was capable of producing either variable-area or variable-density depending upon the particulars of the optical system. Roughly equal measured and perceived quality was available from both systems and from both manufacturers. Neither recording system nor manufacturer was clearly superior to the other, except where specific customer end-to-end processes made one system/manufacturer more consistently superior to the other system/manufacturer. Variable-density was preferred for Technicolor sound prints as this process utilized a silver gray-scale "key" record, thereby creating a CMYK color image, and the soundtrack was also a silver gray-scale record, which greatly facilitated variable-density (and made variable-area rather difficult). The "key" record was deleted from most