CX (audio)
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CX is a noise reduction system for recorded analog audio. It was developed by CBS Laboratories (a division of CBS) in the early 1980s, as a competitor to other noise reduction (NR) systems such as Dolby and dbx. The name CX was derived from "Compatible eXpansion," a feature of the technique.
CX was originally designed by CBS as a noise-reduction technology for vinyl LP records, with a handful of albums released with CX encoding (including Bob Dylan's Blood on the Tracks). CX required a special decoder connected to a stereo system, in order to utilize the CX NR encoded on the LP. However, CX-encoded records could also be played without a decoder, with a resulting (claimed acceptable) amount of dynamic range compression. While this implementation of CX with LPs was quite unsuccessful and short-lived, CX would later see success as the NR used for the stereo analog audio tracks on laserdiscs. It was also used for the audio tracks on discs of the RCA SelectaVision CED videodisc system.
Almost all laserdisc (and some CED) players manufactured since the mid-1980s had CX NR capability as a standard feature, with almost all commercial laserdisc releases having CX encoding on their analog tracks as well.
The theory of operation is described in U.S. Patent 4376916.
