Why no built-in TBC in 1980+ VCRs?

[DVtyro]

I am browsing old video-related magazines, and it is clear that digital in all shapes and forms became very hot in mid-late 1980s, so much so that many VHS VCRs bore "DIGITAL" in capital letters. Sure, they were not D-VHS machines, but had various digital features, in particular PiP and rock-solid freeze frame.

To display a clean freeze frame a VCR needs a frame buffer, which, if I understand it correctly, was the most expensive part of a TBC until mid-1990s, when RAM price dropped 100x within, like, two years. Actually, TBC does not even need a full frame buffer, just several lines is good enough.

But reading reviews of various "super VCRs" that were sold for $1.5-2.5K, I don't see any mention of TBC, why? Was it a deliberate policy and/or agreement of VCR manufacturers with movie studious to dissuade people from copying tapes? Or maybe to dissuade people from using consumer-grade VCR in pro setting? Was it a belief that consumers would not care for TBC but would care for PiP? Anyone has an insight?

Or maybe the models with clean freeze frame had a TBC, but manufacturers preferred not to mention it, again, to dissuade people from using the machines in pro setting?

[ppppenguin]

A very few did have TBCs. Panasonic FS100 and FS200 come to mind. Also the WC-01(?) which could do standards conversion PAL<>NTSC, albeit not very well.

Purely a matter of cost and whether people would pay for it. Since all TVs of that era would lock to uncorrected VCR outputs.

In a pro environment you needed not just timebase correction but also the ability to lock to an external reference.

[DVtyro]

AFAIK, locking to an external clock is needed if several machines need to be synchronized.

How could they implement stable freeze frame without aligning all the scanlines first? Did not they need to have a "frame TBC" of sorts?

Some expensive camcorders like Sony V5000 had TBC, but they were explicitly meant to be dubbed from. And then Sony stopped making them in a year or two, allegedly because pros bought them instead of betacam.

[Electronic M]

I've got an NEC S-VHS deck that I believe is from the late 80s that has digital TBC. It averages frames with 3 different settings and can be bothered by motion or 3-2 pull down from film if set to the most aggressive setting.

An appreciable percentage of non-pro VHS decks didn't start getting TBCs much until DVD recorder combos came out (needed it for dubbing).


In the consumer space it was typically only higher end S-VHS decks that got TBCs in the 80s and 90s, because it was an expensive feature that typically you would only go to after (or along with) the move to S-VHS. The people who bought S-VHS were the only ones who cared enough about picture quality to spend the extra on a TBC, and the number of S-VHS decks without TBC speaks to how many of the S-VHS buyers thought it wasn't necessary/worth the cost.

S-VHS decks can record and play in VHS mode too (S-VHS-ET decks can even record S-VHS signal to the cheaper VHS tapes which is a feature I loved when I was archiving to tape).

Personally if I had to start from scratch I'd look for a DVD-recorder/VHS combo with SQPB, and HDMI like my Toshiba. Then I'd have everything from RF output to HDMI for capture to digital...Like I do now.

[Telecolor 3007]

Originally Posted by ppppenguin

A very few did have TBCs. Panasonic FS100 and FS200 come to mind. Also the WC-01(?) which could do standards conversion PAL<>NTSC, albeit not very well.
.

I think it was the NV-1000.
Never seen one for real. Must have had been very expensive.

[DVtyro]

Originally Posted by Electronic M

In the consumer space it was typically only higher end S-VHS decks that got TBCs in the 80s and 90s, because it was an expensive feature that typically you would only go to after (or along with) the move to S-VHS. The people who bought S-VHS were the only ones who cared enough about picture quality to spend the extra on a TBC, and the number of S-VHS decks without TBC speaks to how many of the S-VHS buyers thought it wasn't necessary/worth the cost.

Sure, and these are the models I looked at. Again: how is it possible to get a clear freeze frame without basic TBC functionality? Did models with digital freeze frame had a TBC of sorts which was not advertised?

[Electronic M]

Digital freeze frame would imply there is a TBC.

If you recorded the tape your self on the same deck playing it you often could get noise free stills, some of the higher spec drive mechanism JVCs without TBC could easily do that even with EP recordings off other models of JVC.
SP noise free stills off of commercial release tapes isn't that hard.
It's EP stills off a a tape recorded on a different deck (especially a different brand) where things get hairy.
Granted I still to this day don't own a flat panel TV, and use a HD-CRT Sony for my HD viewing so if you're watching on an LCD (which often amplify the visual intensity of analog signal noise) we're comparing apples to oranges on viewing experience.
LCDs weren't a thing in living rooms for basically the entirety of VHS' life.

[DVtyro]

Originally Posted by Electronic M

Digital freeze frame would imply there is a TBC.

In this case why would they advertise every other digital feature, but not TBC? It smells like a conspiracy to me Like when the Japanese and, later, Koreans agreed among themselves not to sell dual-cassette machines in the U.S. and not to produce such machines for other brands. They barely won in RIAA vs Betamax case, so I suppose they did not want to advertise a feature that would have improved the quality of copied tapes.

[Electronic M]

Most consumer TBCs were not designed to scrub macrovision copy protection or came with a disclaimer.

[ChrisW6ATV]

Originally Posted by DVtyro

how is it possible to get a clear freeze frame without basic TBC functionality?

A clear freeze frame does not explicitly require digital memory at all. Sony did it in 1981 with their SL-5800, using dual-azimuth video heads.

Pioneer sold its first Laser Disc player with digital video memory in 1988-89, the CLD-3030. That machine only stored one field of NTSC video, so that is an indication of the cost of memory at that time.

It also may be that just storing frames/fields of video is a lot simpler than actually manipulating that memory as needed for time-base correction. That level of information is beyond my knowledge.

[old_tv_nut]

Originally Posted by Electronic M

Digital freeze frame would imply there is a TBC...

Not necessarily. A frame store synced with average V and H phasing would simply reproduce the time variations that normal playback without a TBC had (including possible H phase jump after head switching), and the TV receiver would react to them the same way as in normal play mode.

[Electronic M]

Originally Posted by ChrisW6ATV

A clear freeze frame does not explicitly require digital memory at all. Sony did it in 1981 with their SL-5800, using dual-azimuth video heads.

Pioneer sold its first Laser Disc player with digital video memory in 1988-89, the CLD-3030. That machine only stored one field of NTSC video, so that is an indication of the cost of memory at that time.

It also may be that just storing frames/fields of video is a lot simpler than actually manipulating that memory as needed for time-base correction. That level of information is beyond my knowledge.

Of course on half the Laser discs made that player didn't need it's frame store. On CAV (constant angular velocity) discs where disc speed was constant and one rotation= one frame older LD players would simply skip the laser back one track on IIRC the vertical sync interval of the frame, effectively playing the same frame over and over the way many lower end VCRs do. On later CLV (constant linear velocity) discs where the disc speed changed depending on how far from the center you were reading and the sync pulses of adjacent frames were NOT in the same rotational location on the disc, a frame store was necessary for stills since on CLV there was no effective way to move the laser instantly from the end sync pulses of a frame to the beginning sync pulses of the same frame.

[DVtyro]

Originally Posted by ChrisW6ATV

A clear freeze frame does not explicitly require digital memory at all. Sony did it in 1981 with their SL-5800, using dual-azimuth video heads.

The late 1980s magazines talked specifically about digital features, so it was a digital freeze frame.

Flagging/skewing/hooking is a defect that can originate from mechanical issues, but this is exactly what TBC should be able to fix. This is from 1985. One would expect if not late 1980s then 1990s models to take advantage of digital processing. OTOH, it looks that memory price was decreasing slowly and only dropped significantly by mid-late 1990s.

[ppppenguin]

The whole history of VTRs is a battle against mechanical imperfections.

Quadruplex, with its small drum, could, under ideal conditions, keep the jitter down to 100ns or so, good enough for synchronous monochrome replay. It wasn't easy to avoid banding and other visible errors. The first TBC was Amtec, an analogue delay line with varicaps instead of fixed capacitors. Correction range less than 1uS (I think) but it was enough. Followed by Colortec to get good enough stability for direct NTSC playback.

The frequency spectrum of timing errors on helical scan VTRs was very different. Much more low frequency stuff due to the big drum. Hence hooking. Still all sorts of other errors caused by tape flutter and heaven knows what else. If the errors are bad you get velocity errors along a line which aren't easy to correct.

Colour under was a brilliant kludge to record colour on low-cost VTRs, at the expense of wrecking the delicate relationship between colour subcarrier and H. Didn't matter in domestic environment.

General purpose TBCs had a tough job following all these errors on all sorts of VTRs and tapes. When memory was expensive enough that you only afford a few lines of storage a few early TBCs had a feedback output to drive the capstan motor of the VTR via a power amplifier in order to get true synchronous replay. No idea if this was used very much in practice. I once did it manually with an audio oscillator, public address amplifer with 100V output and a step-up transformer. I could just about keep an Ampex 7003 1" VTR within the correction window of an early CVS517 TBC. But not for very long.

From the early 1990s I designed framestore TBCs for a small company called G2 Systems in the UK. They also did standards conversion, though not to full professional quality. The first versions used dedicated framestore FIFO chips. Later I used first generation SDRAM with an FPGA to give multiport video framestore memory. There were great "get out of jail" boxes in their time. You could stick just about any SD video signal into them (including S video, SDI and in some cases analogue component) on PAL/SECAM/NTSC (and oddballs like NTSC443, PAL-M, PAL-N) and have the output perfectly timed into your vision mixer.

[old_tv_nut]

@ppppenguin, thanks for that info!