[Cin] even more OT: time-base correctors

Fri Oct 1 18:42:03 CEST 2021

Den 28.09.2021 18:36, skrev Andrew Randrianasulu via Cin:

> I read elsewhere [0] you might want such device for bad quality vhs 
> tapes -
> yet they tend to expensive, either in terms of money or skills.
>
> Still, it was pleasure to find some schematic I thought completely lost to
> sands of time:
>
> https://web.archive.org/web/20181219122351/http://marcusgun.awardspace.com/
> newvidproc.html
>
> https://web.archive.org/web/20051101234823/http://www.astro.uu.se/~marcus/private/tbcsch.jpg
>
> [0]
> https://forum.videohelp.com/threads/402960-VHS-recording-advices-would-be-appreciated!/page2
>
> reviews on Amazon tend to be mixed - complex and costly devices do not
> works for some, yet work for others (due to condition of device itself?)
>
> "Short Overview: A time-base corrector is essentially a device that
> reconstructs a composite video signal scan line by scan line. Composite
> video signals (both NTSC and PAL) interlace two fields of lines to
> construct a single frame. With NTSC, you are viewing (approximately) 60
> fields per second, while PAL uses 50 fields per second. Each line has a
> pulse/signal that tells the display device to start the next line. If the
> timing is off even slightly for a single field or for a set of scan lines,
> the individual scan lines don't align with each other and you get a jagged
> effect. A time base corrector tries to correct the timing for the
> individual scan lines to improve the picture. This process never works
> perfectly, but you can definitely see an improvement on most video 
> material.
>
> A full-frame TBC actually stores the lines to build up a single frame and
> then sends them to the video display or monitor. This is preferable to a
> unit that just tries to adjust each line as it is processed. An advantage
> to the full-frame units is that they normally eliminate the copy 
> protection
> signals that are often placed in the unseen scan lines between fields and
> frames. They do this because they insert their own synch signals,
> discarding the "corrupted" ones that Macrovision and other copy protection
> schemes have deliberately inserted. (Yes, I know this is a simplified
> description of a complex process.)
>
> The 8710 is one of a series of TBC units that are reasonably priced and do
> a pretty good job of correction. The improvement is most noticeable when
> you have vertical lines in the picture (telephone poles, lettering, etc.)
> The other features on this unit (saturation control, color correction, and
> so forth) are secondary. It is a full-frame unit and it builds each frame
> using two fields. This allows better alignment of the scan lines and a
> better picture."

I want to confirm from my own experience the importance of using a good 
TBC at the End of the analog workflow from tape source playback, just in 
front of A/D converting and recording.

Especial early generation Hi8 recordings, in the first nineties with 
Sony CCD-TR805 & TR808 camcorders, got unacceptable images with jitter, 
flagging and even dropouts. If this was due to unstable tape operation 
with slippery Hi8 Pro tapes, I don't know. The footages became fine and 
stable with upgrade/replacement to Sony TR-2000 camcorder, still 
functional as Hi8 VCR player).

  * A simple Line based TBC for normal playback were built-in in good,
    reference VCR decks, like my Panasonic FS-200EC S-VHS VCR and Sony
    EV-S880E Hi8 VCR.
  * A full frame or Dual Field TBC was built-in in my Videonics MX-1
    digital videomixer, which resulted in wonderful clear and steady
    analog video images.

As Videonics also published a Digital Video Primer that explained the 
Time Base problems in an easy and useful way, I have scanned and 
attached these 4 pages to this post.

And for further references and reading this old stuff, follow some 
related urls which are still active:

What is a TBC? Time Base Correction for Videotapes
www.digitalfaq.com/forum/video-restore/2251-tbc-time-base.html

What is a TBC* and why would I need one?
https://www.questronix.com.au/tbc.htm

Videomaker
https://www.videomaker.com/article/f3/641-a-tbc-tale
https://www.videomaker.com/article/1210-edit-suite-tbc-trivia

Videonics MX-1 videomixer
https://www.southernadvantage.com/products/videonics-mx-1-4-input-synchronized-video-switcher 

https://www.amazon.com/Videonics-MX-1-Video-Mixer-MX1/dp/B000ZS88N8

Terje J. H

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