Why does the surface of a CED look like an eight spoked wheel when viewed under certain light conditions?
The eight spokes constitute the vertical blanking interval, where the television’s electron beam moves from the bottom back to the top of the screen. The eight wider areas between the spokes constitute eight individual video fields (totaling four video frames). Thus the disc is divided into eight sectors numbered 0 through 7. The vertical blanking interval is used to store DAXI, or Digital Auxiliary Information, a 77 bit binary code that numbers each consecutive field on the disc, divides the disc surface in up to 62 separate bands, and also tells the player if the audio on the disc is stereo, independent channel, or CX encoded (for noise reduction). DAXI is used to update the LED minutes display (and on-screen display, when present), and also prevents the condition of “locked groove,” since the system control microcomputer will advance the stylus two grooves is it fails to receive an increasing DAXI field number.
