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11-09-2022, 07:53 PM
LoftyGoals LoftyGoals is offline
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I've been reading about VHS decode and I'd like to take a serious go at collecting raw data from some of my tapes.

The general idea is to tap the outputs of a VCR's head and run it through a custom board to capture the raw RF signal. The key (for the capture part) is to have a mechanically stable VCR that can track as well as possible.

Ignoring any arguments about whether VHS Decode will ever work or is a good idea, what VCR would you use to read the tape?

I thought it might be the same list as the VCR Buying Guide. The criteria for that list, however, include an analysis of the unit's TBC and post-processing steps. So I thought there might be specific VCRs that are are more rugged, have a better tape transport, etc..

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  #2  
11-10-2022, 12:46 AM
latreche34 latreche34 is online now
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I'm not entirely sure if the RF pull up is final, I've seen inconsistent results from different VCR's and decode hardware, OLN can shed some light here. I know the decode part is not ready for prime time but I have yet to see a confirmation that any hardware and any VCR can pull the exact same raw RF.

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  #3  
11-10-2022, 01:51 AM
lingyi lingyi is offline
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There's a long a active thread at videohelp.com

https://forum.videohelp.com/threads/...-RF-signals%29
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  #4  
11-10-2022, 02:02 AM
lollo2 lollo2 is offline
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I suspect that the 2 aspects (mechanically stable VCR that can track as well as possible and line TBC and good post-processing steps) are paired in a high end machine. I am not sure that you can find an excellent machine for the first criteria and missing the second.

When I will switch to vhs-decode for my captures, I will then use a high end machine as I do now for standard capturing.

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  #5  
11-10-2022, 02:37 AM
latreche34 latreche34 is online now
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In RF capture anything beyond the RF preamp is bypassed, So there is no line TBC, no DNR, No picture setting...etc.

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  #6  
11-10-2022, 05:06 AM
lollo2 lollo2 is offline
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Quote:
In RF capture anything beyond the RF preamp is bypassed, So there is no line TBC, no DNR, No picture setting...etc.
Sure. I meant that in order to have the best "mechanically stable VCR that can track as well as possible" you probably need a high end VCR (which includes useless "beyond RF preamp" circuitery), as asked in the OP.

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  #7  
11-10-2022, 09:36 AM
latreche34 latreche34 is online now
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I see, But there are some good VCR's that have the quality of high end but they are not S-VHS or don't have line TBC, Few models are available from Sony, Philips, JVC, Panasonic. The brands to avoid are the rebranded models, RCA, go video, Funai, Daewoo, Aiwa and the cheap Panasonics.

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  #8  
11-10-2022, 02:21 PM
themaster1 themaster1 is offline
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Any high end vcr from jvc, panasonic, mitsubishi, akai, philips is my guess. One with a good SNR (signal to noise ratio) , because you actually want clear data, not lot of noise over data. On Vcr's manuals they give the SNR generally (mine is : 45 dB, Hr 7700 and Hr-8600ms), other high end jvc's seem to be about the same figure. Panasonic AG-1980P:44dB vhs Sp, 46dB S-vhs Sp)/ Mitsubishi HS-HD2000U: 43dB (vhs Sp), 46dB S-vhs Sp (and more than 46 dB for Ep tapes!)
I'm not sure if this value is for the RF module only or if the heads come into the equation here.

Anyway i've never tried vhs-decode and not a tech engineer.

some good reading:
https://www.electronics-notes.com/ar...nr-formula.php
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  #9  
11-10-2022, 03:48 PM
latreche34 latreche34 is online now
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I doubt it, The SNR figure is for analog outputs video and audio as far as I know. In VHSdecode the crucial part is the stability of the mechanism itself including the heads, its condition (wear), The accessibility to tap to the RF signal and its signal level (different brands have different preamps with different levels of RF), This is the reason I mentioned that RF pull up is not really finalized anything can go wrong and a recapture becomes mandatory.

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  #10  
11-10-2022, 04:39 PM
lollo2 lollo2 is offline
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Quote:
The SNR figure is for analog outputs video and audio as far as I know. In VHSdecode the crucial part is the stability of the mechanism itself including the heads
A RF signal is an analog signal, at radio frequency. SNR ratio is then an appropriate figure of merit for it. However, I ignore if the VCR's numbers provided by themaster1 refer to this RF signal (not sure).
It is also possible, as you mentioned, that the "stability" of the signal is actually equally or even more important for the vhs-decode principle than the S/N ratio, I don't know because I did not study in detail the design.

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  #11  
11-10-2022, 05:01 PM
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lordsmurf lordsmurf is offline
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Quote:
Originally Posted by LoftyGoals View Post
I've been reading about VHS decode and I'd like to take a serious go at collecting raw data from some of my tapes.
Ignoring any arguments about whether VHS Decode will ever work or is a good idea,
But it does need to be stated, understood.

You just need to realize this is alpha-grade tech, not viable now, probably not for years, if ever. In many instances, vhs-decode (or cvbs-decode) is actually worse than what current methods can reliably perform. To some extent, this is for entertainment purposes only, the fun feeling you get from seeing proof of concept in action. The lists of limitations, variables, and caveats is long, and is definitely NOT the path to capturing/ingesting videos with less hassles or work involved. Novices (newbies) fall pray to the "wow, neat!" factor a wee bit too much at times. vhs-decode is definitely one of those times.

FYI, if you're concerned about capture time (as per your other thread), this will far exceed anything you currently imagine. To some degree, it's like building a VCR from scratch, reinventing the wheel. It is a rabbit hole, a time vampire. Video has many of those, if you let it.

Quote:
So I thought there might be specific VCRs that are are more rugged, have a better tape transport, etc..
As stated, the best VCRs are almost all S-VHS models. While most are in a lineage, with lower in their own lineage, some lower units shared lineage with higher. But those shared units also aren't necessarily the units known for solid stability compared to some of the others.

With VCRs, you tended to have junk (with some being "better" junk), and then you had higher end that was embedded in a system to net result in a much better signal. I'm not readily aware of a truly stable units, that isn't S-VHS, and doesn't have integrated aspects. It would have been counterproductive back in the days of VHS to attempt separate functions like this.

Sony and Sharp made some reasonably decent decks, being low end.
Phillips/Magnavox was mid-grade.
JVC and Panasonic made crap for the low-end, ironic since the high-end stuff is some of the best ever made

This is part of why vhs-decode does not work reliably, and may never work, unless hardware-driven additions are made for a kit. It cannot simply be random VCRs with software, it will never work beyond cherry picked tests.

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  #12  
11-14-2022, 12:00 AM
nicholasserra nicholasserra is offline
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Asked how to tap into a AG1980 and nobody really had an answer for me in that thread. Lots of software talk but not a lot of hardware talk it seems.

Anyone finds out, let me know.
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  #13  
11-14-2022, 12:25 AM
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lordsmurf lordsmurf is offline
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Quote:
Originally Posted by nicholasserra View Post
Asked how to tap into a AG1980 and nobody really had an answer for me in that thread.
That really goes with what I've long been saying. vhs-decode is being seen as a way to be cheap, not a way for quality. If it was about quality, we'd be getting info on using S-VHS, D-VHS, and W-VHS decks. Not pawn shop crap. And then there would be talk of TBC appliances, not wishful thinking software (that doesn't exist, and likely never will). As well as custom capture cards, not random pick-n-pull stuff from decades past. Until the project breaks away from cheapskate mindset, it will go nowhere, results will be middling and overall worse than the current standard method.

I sometimes think hodgey/oln is the only project dev that realizes what can and cannot be done, the lone realist in a group of unrealistic optimists and fanboys. He's keeps his head down, does the work, and doesn't blow smoke. So, for now, as it has been for years, the project is mostly background noise to the video capture/ingest ecosystem.

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  #14  
11-14-2022, 06:32 AM
dpalomaki dpalomaki is offline
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Quote:
Asked how to tap into a AG1980 and nobody really had an answer for me in that thread.
Are you seeking to pull the raw Y, C, and HiFi RF from the tape heads during playbacK? If so, Fig 5-22 of the service manual gives the schematic of the head amp which is the place to find it. If that is too complicated it would likely be unwise to mess in the machine at that level. One slip and the machine's resale value could be trashed making it a candidate for an ebay tested but as-is auction.
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  #15  
11-14-2022, 10:14 AM
latreche34 latreche34 is online now
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I second that, Mess with a cheap VCR until you familiarize yourself with the process, It is not just about finding the RF test point, You also need to know what signal level you have, as it was discussed in that thread different levels require different tweaking. That's why I laugh when they say pulling RF signal is 100% possible today and the decoding can happen in the future, but they don't seem to agree on a reliable method or hardware to do so.
Imagine you gather few TBs HDDs and start the process of backing up the RF signal from all your tapes just to find out few years later that the hardware you used had flaws and new hardware is available and better and you have to do it all over again.

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  #16  
11-14-2022, 12:59 PM
nicholasserra nicholasserra is offline
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Meh i'm not gonna trash talk volunteers who are just trying to circumvent the expensve-obsolete-gear market that the capture community currently relies on.

I don't think anyone's claiming this is production ready and a replacement for anything right now. Just people wanting to give it a try, as the possibilities are huge.
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  #17  
11-14-2022, 02:52 PM
latreche34 latreche34 is online now
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No one is claiming the vhs-decode part is ready even the volunteers themselves, We are just discussing the VCR's and RF pullup hardware that they claim it's 100% ready.

https://www.youtube.com/user/latoak34/videos
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  #18  
11-14-2022, 04:49 PM
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Wait, let's back up here...

On paper, this is an interesting project. And if it works as theorized, it will allow for better raw extraction from videotapes. Not just VHS, but others.

But it has a lot of moving parts, lots of variables. At the moment, and for many years now, it's been "proof of concept" with some failures and successes. At best, it's alpha-grade tech.

Do not confuse the videotape RF extraction with the Laserdisc. The Laserdisc project was far easier, as it had more constants, less variables. Laserdisc is, after all, a quasi analog+digital sort of medium. Pristine (as possible) analog date on digital storage.

Like anything else open-source, anybody can participate. That includes sensible folks, and overly enthusiastic folks, or even unreasonble . (At this time, I'd draw your attention to bitcoin/crypto, and all of that BS is currently unraveling as we write/speak. Too much enthusiasm, no realism.)

And in addition to developers, you get fanboys. The loudmouths in the room, the keyboard warriors, the peanut gallery. And most of them barely know how to open up a VCR, much less what everything inside is. Most have never even cracked open a service manual, or a theory book on analog video. So you must learn to tune these folks out. They're background noise. Ignore all the "it's the future!" and "it's working now!" nonsense. Focus on what it is, and what it is not. Learn to distinguish.

Nobody here (on this forum) is "trash talking", we're pointing out the unrealistic overzealous statements that are often made. If you want to dive into this project, awesome. But do so knowing what you're getting into. Don't fall prey to the flowery praise that ignores all the problems and limitations.

Now, back to variables. There's just too many. Way, way too many. The project needs some % of constants injected into it. That means some hardware. It cannot ever function off pure software. At least not if it aims to achieve the potentials.

An issue here is adoption, and the budget and knowledge those adopters will bring. Right now, there's really not much desire to pick apart quality decks, given that it has no real ROI. That's the audience with money and knowledge. (You generally do not see broke with knowledge, nor dumb and liquid.) So far, it's about cheap, not quality, and thus no interest by those that really need to be interested in it. So that's the trajectory. And yet, the project is still too hard for most. So the demographic has been erode from both ends, not quality enough, not cheap enough, too hard. So for years now, it's been in this holding pattern. Anytime several of us mention hardware appliances, we get pushback, and it remains in stasis.

This project is neat, but not yet viable, maybe never viable. For now, I'm neutral on it, and really do not care either way. I just don't want to see newbies suckered by the promises made (and often not even by the project devs themselves) about this homebrew project. And yes, those comments are too often made on Youtube, Twitter, Reddit, and some other places. "It's the future!", blah blah blah.

I try to bring sanity, realism, no BS, to this area of video (capture/ingest). And a bit of quality. That's all.

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