This is a VERY esoteric question, but nerds are often bugged by such.
The CED video player was introduced in the 1980’s and was a competitor to VHS and Laser Disk video. It used a stylus riding in a spiral groove, making physical contact with a capacitive pickup. There was a track-following servo mechanism, a forerunner of the one used in CDs.
One disk revolution would read 4 frames of NTSC video (3 frames for PAL). Since RAM was relatively expensive in those days, a frame buffer for 3 or 4 frames was not affordable. Pausing was possible (the stylus lifted, the screen blanked), but freeze-frame was not. Yet players had a “page mode” where they would repeat the same 3 or 4 frames endlessly.
The only way I can conceive of this happening is if the stylus physically lifted each revolution and repositioned in the previous groove about 8 times a second. Sounds like a bad idea and very tricky to implement. Is this how it worked, or was there a better way?
I know nothing about CED players, but it seems quite reasonable that in “page mode”, they would just use the servos to keep the stylus in place and have it more or less skip. It may not have the best for the disc, but for short periods, it would not make a difference. Remember, using the “pause” button on VCRs causes the read head to continuously rotate against one section of tape (to its long term detriment).
If you read the paragraph right after, it states that a mechanism to skip forward and backwards between groves is in all the players that do page mode. Apparently, it is in fact picking up the style a little and moving over 1, just like you thought.
Just read about CED players for the last 30 minutes. There has to be a mechanism to pick the stylus up and another mechanism to move the carrier containing the stylus around, or the player itself would not work. So, this “page mode” can be added to a player merely with additional control circuitry to drive it.
The tradeoff matrix for them was
Lower cost to manufacture the players and the disks vs vhs/laserdisk/betamax at the time.
Could not record to the disks
Inferior video quality compared to laserdisk, the other playback-only format. Also, the disks would degrade with each viewing, while laserdisks won’t.
As an engineering concept, a forced 1-track skip sounds like a bad idea. Think of the damage done to a vinyl LP when that happens. Of course, vinyl is softer and the stylus pressure greater on an LP. I wonder if the manual ever warned users to avoid staying in that mode for long.
I remember when that player came out. I thought the whole idea of a physical tracking device pretty retro when lasers were already being used, so it was never on my Christmas “must-buy list.”
Yes, I saw that, but pressing a button and having the stylus lift and shift doesn’t sound like it had to be accomplished in 1/8 second, while the “staying in place” mode has to happen fast and repeatedly, and the higher the stylus was lifted, the longer it would take; the less it was lifted, the more potential for damage. Maybe the servo was just sophisticated enough.
I own one of these and mine does not have that function, I wish it did. Mine is cranky and works about half the time but I do love it, crappy picture and all.
As you note, the tracking force on CEDs is much less and they do not actually use the groove sides for information, but for tracking. Since VCRs already had the problem of damaging tapes when left in pause, I do not think most people at the time would consider it a defect if CEDs were similar.
The description you quoted makes it quite clear that is how it worked.
Despite being digital, They did not store even one frame in RAM, they pushed the bits of info out to the video output just as soon as they read them, and so the only way to freeze-frame pause is to physically skip back one groove.
Wow! We had one of those back in 81 or 82, it didn’t last long and alot of movies weren’t really available.
Oh yeah? I wore out our copy of Airplane!, Saturn 3, and Last Tango in Paris by pausing all the nude “bits”
I don’t think the stylus is actually picked up at all. My understanding is that the paging simply locked the tracking carriage in one position forcing the stylus to repeat same 3 or 4 frames in that revolution then “skip” back into the same groove.
The stylus is simply permitted to “ride” over the ridge into the previous groove.
The light tracking force controlled by an array of sensors, deflection coils, etc., plus the keel-shaped stylus and its tangent all would minimize any physical damage.
The information is at the bottom of the groove so the only possible damage would be to the ridges or the titanium stylus.
I suppose wear could occur if paused for a extended period but normal usage would be for short periods and unlikely to occur exactly in the same precise spots on the disk.
Unless, of course, those 3 or 4 frames are of Boobies!
