Why no built-in TBC in 1980+ VCRs?
 

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?

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.

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.

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.

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

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?

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.

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.

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

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.

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.

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.

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.

https://i.ibb.co/0FW4tZ0/hooking.png

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.

@ppppenguin, thanks for that info!

Which is why it seems to me that it made sense to build a TBC into VCRs themselves, at least into expensive top level models, as manufacturers shoudl have known better what sorts of errors their machine produced. Ah, well.

Adding a TBC to a home VCR would produce little or no improvement to the picture on a home TV set.
Large incremental cost + miniscule incremental improvement = not worth it

The clipped Q&A from a 1985 magazine I attached above was about skewing on some tapes, a defect, which is usually mitigated by a TBC. I have some tapes that show this defect, some of them I can play on my machine that has built-in TBC, and the frame comes out straight. Problem is, the machine plays only in SP mode, so cannot play crappy EP tapes on it.

So, TBC is not just about jittery image, but about fixing more glaring issues, in some cases it can make barely playable tape look just fine.

But I hear what you are saying - in most cases it would be useless unless someone used their VCR for dubbing, especially in the time when TVs were flickery 60 Hz interlaced, not something like 120 Hz with built-in deinterlacers.

A frame store is not a time base corrector and this doesn't necessary imply that they are inclusive to have one or the other.

I know that a frame store is not a time base corrector. I just thought that a storage is the more expensive part of a TBC, and since the VCRs in question have one, then maybe having a TBC would put this storage to a good use. Apparently, I am wrong. Thanks.

After about mid-1981 or so, probably 99% or more of Laser Discs were Extended Play (CLV), so that feature was a real treat to have.

When a description of a VCR reads, "extremely stable horizontal phase lock minimizes flagging at the edit points," does it mean a built-in TBC ("line TBC"), or does it mean a precise servo control with loop back, which may ensure straight left edge of the frame, but does not compensate for velocity errors, so the right edge may be jagged?

I have a late model Panasonic VHS that has a built in TBC.
Have you ever heard of an ADDA ESP2? That was a sweet little box. It would do everything!
It was a 2 channel Frame Sync, Still Store, or DVE (digital video effects) depending on what mode you used it. Unfortunately it was an 8 bit box so it was a little noisier than the later 9 and 10 bit boxes. The one at our station lost a channel. Nobody knew anything about it. So, on a hunch, I changed the Z80 microprocessor and that got it back!
Haven't seen any for quite a while. So people who have them are holding on to them.

Sorry to get off topic.
My Heathkit GR2000 had a rough time with off-tape sync. Too much flagging at the top of the picture. Some tapes were worse than others. BUT I found some sets had absolutely no problem with off-tape sync.
There are 2 things to remember about tbcs's. One is quantizing and the other is sampling. Quantizing is the number of levels an analog signal is chopped up in the A to D process. An 8 bit box will slice it up to 256 levels. A 9 bit box would slice it to 512 levels . And a 10 bit box would slice it to 1024 levels. Obviously the more levels would provide greater "resolution" of the signal, but at the expense of requiring more memory.
Sampling is the rate of conversion. Early tbc's were 3fsc (about 10.7 MHz.) and later ones were 4fsc (about14.318MHz.). Requiring a faster memory.
Low end tbc's were 8 bit. Ampex tbc's were 9 bit. Sony and Tektronix were the Cadillacs at 10 bit.

With the amount of noise comming off tape, 8 bits is entirely adequate for a TBC. The noise acts a dither signal which makes quantising errors invisible. This is true for any analogue to digital conversion of any signal, not just video.

I did some experiments many years ago with reduced numbers of bits. Even 1 bit (yes, one bit) with lots of random noise gave a picture without quantising effects, though I had to add a horrible amount of noise to get there.

The problem in early TBCs was the ADC rather than memory. Until the TDC1007 was invented, 8 bit video ADCs were very complex and expensive. That chip won an Emmy aawrd in 1988. It was still several hundred $$$. Then the price of ADCs rapidly came down.

There was a lot of work done with sampling locked to colour subcarrier. This had some benefit but ultimately it's a lot better if the samples line up in a rectangular grid. For 625 and 525 systems the "601" standard settled on 13.5MHz to sample luminance. A lot of older systems sampled at 10 to 12 MHz.

I remember when 16K of RAM was in the hundreds for my Apple IIe back in the 1980's so imagine what that would be for a home grade VHS or Betamax VCR to do say a field of video, I'm not counting the ADC & DAC or any of the interface circuits to make it happen. My dad replaced our Sony top load Betamax with a new Hitachi VT-98 VHS HiFi in early 1985 for something north of half a grand. The HiFi added a few hundred bucks to the $299 base price of the low end VT series. I can't imagine what it would cost to have a real TBC in those days.
I will say it was a good investment as the deck still works today with only a recap of the supply.

FYI the sticker price of a MicroTime 2020 TBC was in the tens of thousands in 1979 and a FOR-A FA300 was about the same in the late 80s. I was involved with a school production studio and wrote out the acquisition request so we could feed the city cable system, they choked on the price.

RAM sure was expensive, but by 1985 it became affordable. Here is a RAM price chart from 1970 to 2000:

https://i.ibb.co/89LYcdv/RAM-cost-1970-2000.png

Or, in numbers:

1970 - $734,000/MB
1975 - $50,000/MB
1980 - $6,000/MB
1985 - $300/MB
1990 - $46/MB
1995 - $9/MB
2000 - $0.7/MB

Late 1980s VHS had "Digital" written all over them. With PiP and digital freeze frame I presume these machines already had ADC and DAC.

1MB is needed for a full-frame storage, so $300 in 1985 was doable for a high-end machine, even cheaper by the start of the 1990s. I would expect high end SVHS machines to incorporate this feature as standard, too bad this did not happen.

The jump from MBs to GBs for RAM happened so quickly I barely noticed it. My 1998 laptop has 256 MB of RAM. My next desktop had, I believe, 2GB.

Problem is most people didn't care about all the extras when their goal was rental tape playback and recording reruns in SLP mode, a TBC would only add to the confusion of the cheapskate owner whos clock perpetually blinks 12:00... the same guy who thinks his 13" Portland TV is the best on the block.

My Sony Digital Betacam (A-500/1) has a framestore system for BetacamSP analog playback. The head diameter is slightly larger in the digital decks so everything is transcoded digitally, timebase corrected and stored then buffered before feeding the video DAC, it also feeds the SDI port.

My two cheap early 2000s camcorders, PAL VHS-C and NTSC SVHS-C, have built-in TBC. This has been captured from the NTSC one: https://youtu.be/Lge8hlQrCLw Many Digital8 camcorders have built-in TBC, which is used when playing back analog recordings.

The Digital-8 I believe does a similar transcode as the Digital Betacam on a smaller scale and going digital gives perfect timing by nature. In retrospect it's too bad the Digital-8 format didn't make it past the consumer market before the other DV formats took center stage. I have both DVCAM and DVCPRO and they run a much smaller head than the original 8MM. Timing isn't so much an issue here as it is dropout count, personally I feel the later DV format relies too much on the memory to fill in the dropouts than if it was mechanically more robust. It doesn't take much to cause a digital blip with the smaller tapes, far less than the Digital-8 which was back compatible with the Video-8 & High-8. Guess Sony was onto something here.
I can't speak for the VHS camcorders as I have always gone to great lengths to avoid the format in general but Panasonic did have some high end "prosumer" decks in the NV model line that had a very good TBC. As the format itself was geared for the home market very little was developed and refined for the more demanding broadcast and production arenas, unfortunately it takes more than a good TBC to bring the format to a level required for prime use.

I have been asking this question for a while: why develop a completely new cassette family for DV instead of using existing ones, like Betamax for Betacam or VHS for M, and I could not find a definitive answer. Versions I considered and rumors I came across from other people so far:

• DV cassettes could be scaled easier than, say, 8-mm cassette.
• DV tape is narrower (6.35 mm or 1/4-inch) than 8-mm, so tape savings and thinner cassette.
• MiniDV cassette is much smaller than 8-mm cassette, which means more compact recorders, but then again, could 8-mm cassette be scaled down?
• 8-mm cassette would not have enough recording time (in practice, 40 minutes on 8-mm cassette vs 60 minutes on MiniDV is comparable, and in the olden days ENG cassettes were 20 minutes anyway).
• Probably the biggest one: JVC and Panasonic agreed to join DV if it would be a new format for everyone including Sony, so everyone would be in the same position. Panasonic made 8-mm machines for other brands, but not under its own name. JVC, I believe, made none. So, they did not want Sony to have competitive advantage with 8-mm cassette, otherwise Sony could take, say, the CCD-VX3 (VX1 in Europe), replace analog encoder with digital, and voila! Instead, Sony had to rip out the 8-mm transport and install MiniDV transport to create the VX1000. If this is a true reason, I wish JVC and Panasonic were less vengeful.

JVC and to lesser extent Panasonic aggressively marketed SVHS towards pro market when M and then MII fizzled. In some aspects SVHS is better than Umatic, all it needed were pro connectors to integrate it into a plant. Pro-looking VTRs, consoles, TBCs were made, SVideo as well as Dub connectors, including provisions for timecode and I believe there were even claims of 1-frame precision editing.

There is still the issue of the hetrodyne color under used by S/VHS, Betamax and Umatic that limits the color resolution to about 30 lines give or take so while the actual luma detail may be higher in the S-format there were still logistical challenges in the broadcast world wired for composite. The only real reason the M format fizzled is Sony had already established the Betacam format in the broadcast arena, sort of like a beta revenge despite the M format being technically superior in several aspects. That being said you're right on the mark regarding the modern DV technology as both Panasonic and the founder of VHS JVC didn't want another format monopoly. My biggest bitch is with tape compatibility. The Sony DVCAM decks will accept both a large and small DV tape without an adapter but Panasonic requires a difficult to find adapter to run both consumer and professional small DV tapes in their DVCPRO decks... thought we learned a lesson with VHS-C. Sony runs the DVCAM tapes faster than DVCPRO but does not have the linear cue track. I have a Sony DSR-50 portable that I use as both a 1394 feeder and 4-channel DAT for capturing older quadraphonic material plus two DSR-1 docks on D-55WS cameras for DVCAM and Panasonic AJ series for DVCPRO, one SD-755 and HD-150 along with two Sony DVW-A500/1 Betacam decks. they're from my "classroom in a can" days of technical training production that has been taken over by amateurs on YouTube.


I do have a Panasonic AG-7500 SVHS editor with "most" of the pro connectors, RCA audio rather than XLR and while its been a good deck I found U-Matic to "look" better on the screen than an S-tape running side-by-side.

The first one I ever saw was a CVS-504. It used digitally switched glass delay lines. It had 2 modes of operation-direct and heterodyne. The heterodyne mode looked awful but the direct mode looked pretty good. CVS won an emmy for it!
Stations loved them. They were able to get out from the expensive yoke of quadraplex.
The one I really liked was the DPS Phaser 1 (and later Phaser 2). It was made by Digital Phaser Systems out of Toronto who was later bought by Scientific Atlanta.
It would take any old crappy signal and make it broadcast-able. I remember live shots, that were falling apart, and we put them on the air.
It would make chicken salad out of chicken$#!+.

M and Betacam were shown at 1981 NAB simultaneously, but M was production-ready, while Betacam still was a work in progress. M had about half a year lead time. It just was not as good as Betacam.

Do not discount amateurs, they have a desire to learn, show and tell. Also, many of them are quite knowledgeable. Dave 12voltvids is a former video engineer, so not an amateur. But Colin (video99.co.uk) did not work in the industry, AFAIK, but I don't know for sure. Also this Vietnamese guy is very good: https://www.youtube.com/@misu4602 (his videos have English subtitles).

What do you mean by "direct mode"? AFAIK, 2-inch had their own built-in mini-TBC, controlled with knobs and dials.

I thought that fixing crappy Umatic (heterodyne color) and earlier B/W portapaks (no color, so cannot be called heterodyne, can they?) was the primary reason for TBC. If Umatic looked awful, how CVS could win an Emmy for it? Could you clarify, please.

Do keep in mind a TBC corrects the entire timebase of the video signal not just the chroma irregularities regardless of the format be it an EIAJ Sony AV-3450 B&W PortaPack or Sony BVW-75 BetacamSP even the Type-C format had a timebase corrector. Think of the scan lines as a deck of cards all stacked up, the TBC just centers all the cards so all the edges are nice & neat. Color correction is more of a Proc Amp that can manipulate the chroma & phase along with the positive & negative levels of the actual signal.


Going back to your previous post I'm not discounting the amateurs for a lack of knowledge, they just put me out of a job. Some of them are quite talented and others are learning as they go, the cool thing about knowledge is everyone can learn and expand themselves. My dad and I were technical writers and we produced countless training videos together, he wrote and I captured and we both edited everything together to make the final production.

The M-II format was actually far superior than the BetacamSP format in many aspects but Sony had already established the "oxide" Betacam format leaving Panasonic in the dust, M-II was the M format after puberty.

Quads had 3 timebase correction systems. The first was automatic guide servo which corrected gross errors at the headwheel. On early machines this was a manual adjustment. The second was MATC mono automatic timing corrector. The third was CATC color automatic timing corrector. Some machines had CAVEC which corrected hue banding across a head.
The later machines like AVR3 and TR600 had digital TBCs.

As I recall M2 format was a full bandwidth analog system. I saw a demo once and it was outstanding!
Some stations even bought the M2 automation system for commercial playback! No stations in this market but there was one in Augusta GA. that had it!

There were some PBS stations and I believe the BBC dabbled in the M-II format for a number of years but eventually dropped the format in favor of BetacamSP and D2. My quad experience is limited to an AVR-1 during my Studio North days... what a monster!

I am re-reading this thread. I guess this was important to why TBC were not commonplace until the late 1980s:

An article from 1987 reads:

I don't think that in 1987 256 KByte chips were readily available. I think the author meant 256 Kbit modules. Looking at John C. McCallum memory prices, I see 256 Kbit modules. If six modules are used to store a complete frame, then it is 192 KB for the whole frame. How? I guess they did not use the full Rec 601 frame, but a low-res one that would match VHS. Say, 480 * 240 = 115200 elements. With full 8-bit color it would be 115200 * 3 = 345600, this would not fit. But with halved color it would be about 170 KB, good enough for a freeze frame, but I suppose they figired it was not good enough for a proper TBC.

An interesting observation from the memory price data: in 1987 RAM price price was about $160/MB, but next year it jumped to $500/MB! It fell back to $120-180 by the end of 1989, but I think this spike spooked VCR manufacturers, so they scaled down on digital features. They probably also figured that PiP and clean freeze frame were not really popular.

By 1990 RAM price dropped below $100/MB. An article from 1990 was hoping for TBCs to become more common, claiming that "top decks adopt a picture-fixing feature".

Early DRAM was rather slow. In any case you need both write and read at video rate. The solution was in two parts. The first is to demultiplex the video. So 8 bit video at 13.5MHz (the 601 rate) might be demuxed on to a 64 bit bus at an eighth of the speed, under 2MHz.

The other need was to alternate read and write cycles (It's rather more complex than this. I know as I've designed video framestores with multiple video read and write channels) so time slots have to be allocated.

There were also special memory chips for video line and frame stores. Typically these worked as shift registers so no complex addressing needed. For example NEC had a range of linestores including the upd42102. Averlogic had the AL422 series of framestores. Nice chips, easy to use, but much less flexible than DRAM. In my own designs for clients I did a lot with first generation SDRAM. All the addressing, multiplexing, access arbitration etc was in Xiinx FPGAs.

Some early TBCs used fewer than eight bits. I think the CVS517 from the late 1970s used 7 bits https://worldradiohistory.com/hd2/ID...-Page-0232.pdf There may even have been a 6 bit TBC from a small UK company whose name I forget. If there's any noise on the input video it acts as a dither signal which makes the number of bits less important. I even once built an experimental 1 bit framestore. The monochrome picture was, of course, awful. In coloured areas, the high amplitude PAL subcarrier acted as a dither signal and gave surprisingly good pictures.