November 1986 Video magazine reports on the first VHS VCR with digital features, tested by the magazine - RCA VMT-400.
So, there is a 300KB buffer inside a $700 machine. This is enough for a whole field with 4:2:2 color.RCA’s VMT400 uses an analog-to-digital (A-to-D, or A/D) converter to transform analog signals to digital form, a 2.4 megabit dynamic random access memory (DRAM), and a digital-to-analog (D/A) converter to transform the analog TV signal to the digital domain—storing or processing it—and recreating a recognizable picture. These steps let the VCR deliver the following effects: picture-in-picture, the ability to move the inset to any corner, picture swap, rock-steady still frame, distortion-free slow motion, cleaner search, and the ability to freeze the action from the tape or a broadcast, digitize, and colorize the picture.
This is the first VCR with digital enhancements we've tested. Freeze, still, and slow motion pictures are noise-free but some show a very slight vertical jitter. The frozen picture offers about the same resolution as the moving picture, but attempts to measure the various signal to noise ratios yielded numbers much worse than our eyes led us to believe. A closer examination of the noise showed traces of timing pulses too small to see in the picture. They falsely affected the S/N readings. The inset had a horizontal resolution of about 200 lines. Its S/N could not be measured separately.
From the March 1987 issue:
So, a million-dollar question: why TBC is not listed in the features above? I thought that RAM was the most expensive component, and this VCR has enough RAM for a full-frame TBC, and it had A/D and D/A converters for clean freeze-frame. They say they noticed traces of timing pulses? Meaning, the freeze frame was not rock steady? Even if this were true, it sure should have been more steady than the picture taken directly from tape. And then there was a flurry of other "digital" VHS VCRs that had rock-steady freeze-frame, which implies that they had a TBC that worked at least for a freeze frame.RCA’s VMT-400 has nine 256 Kbit chips, arranged to provide sufficient memory to hold two separate fields of color video data. Two of the DRAMs are dedicated to the picture-in-picture feature, while six more are used as the main memory for the freeze, mosaic, and posterization (or “paintbrush”) special effects. The last chip is used to process synchronizing signals.
So, did those "digital" models actually have built-in TBC, but did not advertise it for some reason? Or did they have something else, which was very close in functionality, but worked only for a freeze frame? If the latter, then why? Why not making a proper TBC for an extra, I don't know, hundred dollars? These TOTL machines were close to $1K anyway, so their user base would definitely appreciate a TBC. Or was it a part of an agreement with MPAA to not improve picture during playback, because MPAA was afraid of people copying their tapes?
Was VHS considered less attractive for copying after DVD came out, so that manufacturers felt that it finally was ok to install built-in TBCs in the late 1990s? The whole thing is fishy.
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Last edited by Bwaak; 24th Aug 2023 at 01:26.
Here is one from 1989 for $1900, ouch.
What's your dilemma with TBC? Manufactures have always used proprietary technical terms for the features they design, They even sometimes try to avoid it in the fear of leading to potential legal battles with other manufacturers and we've seen it happened. Sony never mentioned the word TBC in any of their VHS/S-VHS VCR's equipped with digital processing using a memory buffer except for one or two high end machines sold in Japan, The ED beta machines have only digital pause, no analog pause but there is no mention of TBC anywhere in the manual.
Maybe the digitizing circuitry didn't do a good enough job at stabilizing that it was worth it being active during normal playback maybe compared to how it would be handled by the TV? Or worse for that matter. It could also be that it would have caused issues with tape dubbing for all we know if it was active during normal playback.
It was not really a feature that had that much use on a consumer vcr until it was combined with more advanced DNR processing to improve image quality but by then VHS had kinda started to be supplanted by DVD already. The fact that it's useful for digitizing is mostly due to almost no capture devices featuring the hardware to stabilize video themselves (or capability to offload some of it to let the computer do it in software) even though the tech definetly exists as seen in e.g panasonic dvd-recorders. CRTs other than very early ones usually handled videotape input sufficiently well on their own so there wasn't much purpose to add expensive memory buffers and digital processing to vcrs other than as a fancy gimmick or for serious editing purposes until it became somewhat affordable.
But all this is not what I am curious about. I am wondering that in the mid-late 1980s digital started to become the thing, and many VHS machines were labeled "digital" and they already had "expensive memory buffers and digital processing" necessary for implementing a TBC, thus a question:
* was TBC or something TBC-like indeed implemented in machines that had digital freeze frame?
* why TBC was not advertised as a feature, if it was implemented?
Well, the Philips machine advertised it as the means to reduce jitter and distortion.
Last edited by Bwaak; 24th Aug 2023 at 12:29.
If you watch a home-recorded analog tape, such as VHS, you will find there is always a distortion between scenes/recordings and that's because there was no synchronization between the two.
CRT TVs, including old ones, can handle this well, no problem.
As for broadcast vtrs, if you are talking about open reel formats like quad, b-type and c-type those were full composite formats rather than color-under like VHS, betamax and the like so in addition to the mixing aspect and needing a stable output signal they were quite different to what you would get from a home vcr. Quad and b-type also used multiple tracks per field while c type literally didn't record part of the vertical blanking area possibly to save space and had to reconstruct it during playback so required specialized TBCs working with the gear.
A VCR with digital freeze frame would need to have a buffer for video data but it might not have extra stuff to delay and adjust the timing of the output video to compensate for jitter, or maybe only to a smaller degree than a purpose built TBC module. I haven't looked into it in detail though.
I have two VCRs that are like that, the EV-C2000e 8mm VCR and the Samsung SV-7000W. The latter can engage the digital buffer during playback but it only does if system conversion is active or if you use the "art" function (posterization and strobe special effects). It's not capable of jitter correction to nearly the degree SVHS VCRs with TBC are though, it actually uses the same SAA7113 video decoder chip as found in some older capture dongles like the dazzle DVC100 though unlike in those it doesn't cut out on bad signals, and it also seems to blank VBI. Haven't really looked into what degree the digital stuff int he 8mm vcr corrects jitter and whether it's anything comparable to it's bigger brothers that do advertise a full on TBC/DNR unit. VCRs could also have DNR without any sort of TBC function.
Should also note that digital was a bit of a buzzword in the late 80s/early 90s also, so a vcr having "DIGITAL" on it could just mean that the tracking system was digitally controlled which became standard at one point.
The whole TBC term is a bit muddy in general though, so I prefer to talk more about what the device/module is actually capable of and does than what it's labelled as.
Last edited by oln; 24th Aug 2023 at 17:21.
Altenatively, frame synchronizers can sync two or more videos, they align V-Sync pulses. Because they buffer the incoming video, they introduce delay.
Either way, this is not what TBC is about.
Last edited by Bwaak; 24th Aug 2023 at 19:32.
Originally Posted by Bwaak
Agreed, what matters is the function -- and an advertised function operating as stated.
Thus some items not labeled "TBC" are TBCs, and some labeled as "TBCs" are pure hogwash.
Charlie Munger: "If you're not a little confused about what's going on, you don't understand it."
From Video magazine, January 1990:
Panasonic’s PV-S4990 boasts a wealth of features at a reasonable price. Its most impressive feature is a switchable time base corrector (TBC) that straightens out ragged vertical lines. No mechanical transport is without some slight speed instability, and a TBC can correct the problem.
From Video magazine, April 1990:
Philips’ top VCR is a Super VHS model, the VR6995ATO1. ... The VCR has a large number of helpful and unusual features. Foremost is a time base corrector (TBC), which straightens out vertical lines made ragged by slight speed instabilities in the mechanical tape transport. TBCs are still extremely rare among consumer VCRs.
I am posting these just to keep track of some VCR models with TBC, no need to respond.
I was going to write 1990 in my above post here, along with exact RAM pricing in 1990, but I couldn't find what I wanted, so left that part out. I was fairly certain 1990 was the date, and that 2mb was "large". We had just upgraded to a 386 at the time, and splurged for 4mb RAM. I just looked again, and it looks like 2mb would have been about 1/3rd the cost of the VCR.
Just remember that Video magazine was for consumers and hobby, so don't expect in-depth tech explanations. Many authors (mostly journalists) of hobby magazines only had decent competence back then, not necessarily true expertise or mastery of the subjects. And many of the articles were just rewritten press releases, which were themselves not written by techs. The technical is gobblygook technobabbly to most, so it can get lost in translation to normal English, sort of like the telephone game.
Trivia: I think that June 1990 article was written by a somewhat well known hobby writer (but non-video) in his early days
Tip: When you research, look deeper.