RCA Photophone - Comparison of (mono) Variable-area and Variable-density

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 axis was parallel to the film motion. 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 sound track 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 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.