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3.14 Why does the surface of a CED look like an eight spoked wheelwhen viewed under certain light conditions?




Description

This article is from the RCA SelectaVision VideoDisc FAQ, by tom@cedmagic.com (Tom Howe) with numerous contributions by others.

3.14 Why does the surface of a CED look like an eight spoked wheelwhen 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.


 

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previous page: 3.13 Is it true that RCA VideoDiscs will be unplayable once thecoating on the disc surface evaporates?
  
page up: RCA SelectaVision VideoDisc FAQ
  
next page: 3.15 What is recorded on the unused sides of CED's?