Quote:
Originally Posted by old_tv_nut
The disc output is continuous through vertical sync
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There was a crude attempt to reduce the time base errors in the CED players. There was a feedback mechanism that moved the pickup stylus perpendicular to the direction to the disc's center. They used what was essentially a speaker voice coil as the driver of this stylus mover. This was to counteract errors due to poor disc centering and turntable wow and flutter. But feedback loops reduce but not completely remove such errors, if they tried they could overshoot and go unstable.
Early CED players used a synchronous AC motor fed by the 60Hz powerline, so the disc would rotate at a speed to produce vertical sync at 60Hz. The color subcarrier was recorded on the disc at around 1.53MHz, and the player would upconvert that to the 3.58MHz NTSC standard, using a beat oscillator around 5.11MHz. The above time base errors would also show up as subcarrier frequency errors, so the beat oscillator frequency was FMed to counteract that, to produce a stable NTSC 3.58Mhz subcarrier.
Back in the day, TV sets' horizontal was designed to cope with erratic horizontal sync from VCRs.
DVD players use digital FIFO buffers and frame store memories, and they control the disc spin rate to keep these buffers and memories half full, and thus produce precisely timed video.