Why no built-in TBC in 1980+ VCRs?

[DVtyro]

Originally Posted by ppppenguin

General purpose TBCs had a tough job following all these errors on all sorts of VTRs and tapes.

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.

[old_tv_nut]

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

[DVtyro]

Originally Posted by old_tv_nut

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.

[ARC Tech-109]

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.

[DVtyro]

Originally Posted by ARC Tech-109

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.

[ChrisW6ATV]

Originally Posted by Electronic M

Of course on half the Laser discs made that player didn't need it's frame store.

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.

[DVtyro]

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?

[kf4rca]

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.

[kf4rca]

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.

[ppppenguin]

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.

[ARC Tech-109]

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.

[DVtyro]

Originally Posted by ARC Tech-109

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.

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



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.

[ARC Tech-109]

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.

[DVtyro]

Originally Posted by ARC Tech-109

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.

[ARC Tech-109]

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.