Current status of ld-decode / vhs-decode (true "backup" of RF signals)

[lollo]

Brad, for conventional workflow use ATI 600 USB if you can

[nicholasserra]

Also on my list to do this comparison. I dove in a month or so back but did not get good results from the capture. Very large rabbit hole to go down

[Brad]

Also on my list to do this comparison. I dove in a month or so back but did not get good results from the capture.

Turns out, I'm also getting bad results attempting to RF capture from AG-1980.

The amplitude is just awful except for a retail release I tried (Beast Wars tape 4). More importantly, all of the captures feature the famous crosshatch issue prominently.

I'm not particularly interested in spending time solving this, since I'm already getting clean captures from other VCRs.


@dellsam34 Would Mitsubishi HV-BS890 count as high-end? It includes DNR and "629TBC" seemingly licensed from JVC.

[nicholasserra]

I need to crank up the gain on the DDD and try again. It's all sitting right here on my desk but too many other tape projects keeping me busy

[lollo]

@dellsam34 Would Mitsubishi HV-BS890 count as high-end? It includes DNR and "629TBC" seemingly licensed from JVC.

Why do not make a comparison between the capture of the Panasonic AG-1980 + ATI 600 USB and the capture of VHS-Decode with a VCR of your choice (it does not have to be the Panasonic AG-1980)?

[dellsam34]

Mitsubishi HV-BS890 should be good, Can you use it for both methods? I read about 629TBC feature, Anyway, don't you have to compensate for the Japanese IRE levels when playing back US NTSC tapes?

[Brad]

I'll try to tap the HV-BS890 then. And I can include the AG-1980 conventional as a third source.

don't you have to compensate for the Japanese IRE levels when playing back US NTSC tapes?

Nope. Similarly, if you play an NTSC-J tape in a US VCR, it won't have US levels.

@nicholasserra My DdD is always at max. But it is possible to swap out resistors for additional gain, if you want to modify your DdD and can handle surface-mount soldering.

[vhs_cap]

Now then,

After having done research for considerable time and read through vhs-decode wiki a couple of times I still got some unanswered questions, I’d be very glad if someone could answer them as I’m not a VHS, electronics or signal expert. And please, no ”it depends” or ”test by yourself” to every question.

THE TAP SIDE:
1 – Is the usual test point location fine or is direct head tap the ”Holy Grail”?
2 – Can tap points be tested before soledring with a simple ”clamp-to-BNC wire” and USB SDR stick? Of course bandwidth will be limited but my plan was tap the decks now and build the capture hardware later?
3 – Can or should you tap a Sony-DuPont deck with a soldered tap?
3- Will there be any harm if I put a capacitor on RF tap ”just in case”?
4- Do linear and HiFI audio have different tap locations or will a single tap do? Or can/should linear audio even be RF tap’d?
5 – Pre-amps, yea or nay? There seem to be many options from off-the-shelf options (ADV8367 & general SDR amps) to full custom ones (Rene Wolf amp). Is there a strict SNR dB value where you should or should not use one?
6 – At the moment I have only SCART decks, do I get better reference capture quality if I do a ”RCA tap”?

THE CAPTURE SIDE
1 – Are CX card mods necessary? How much do I gain in quality if I do the BNC mod, C31 mod and 40Mhz crystal mod?
2 – Can I somehow sync audio without (drift) issues without clockgen mod from RF audio capture or should I just capture only RF video and use audio track from conventional capture?
3 – Is there any point capturing head switch singnal with third capture card?
4 – Do I need a expensive & hard-to-find CRT monitor to check tracking or can it be done in some other way?
5 - There seems to be some new USB RF hardware in development, will it be worth the wait aka considerable upgrade to CX cards?

Oh, one more, don't laugh at this, I haven't touched a VCR in 20 years: I have some "non-important/whatever/dontcare" tapes which I'd like to capture but I'd also like to keep them recordable by not breaking the tab, can I trust my VCR & VCR operator skills to not record over them in capture process? (I said, don't laugh!)

Thanks in advance.

[harrypm]

Now then,

After having done research for considerable time and read through vhs-decode wiki a couple of times I still got some unanswered questions, I’d be very glad if someone could answer them as I’m not a VHS, electronics or signal expert. And please, no ”it depends” or ”test by yourself” to every question.

THE TAP SIDE:
1 – Is the usual test point location fine or is direct head tap the ”Holy Grail”?
2 – Can tap points be tested before soledring with a simple ”clamp-to-BNC wire” and USB SDR stick? Of course bandwidth will be limited but my plan was tap the decks now and build the capture hardware later?
3 – Can or should you tap a Sony-DuPont deck with a soldered tap?
3- Will there be any harm if I put a capacitor on RF tap ”just in case”?
4- Do linear and HiFI audio have different tap locations or will a single tap do? Or can/should linear audio even be RF tap’d?
5 – Pre-amps, yea or nay? There seem to be many options from off-the-shelf options (ADV8367 & general SDR amps) to full custom ones (Rene Wolf amp). Is there a strict SNR dB value where you should or should not use one?
6 – At the moment I have only SCART decks, do I get better reference capture quality if I do a ”RCA tap”?

THE CAPTURE SIDE
1 – Are CX card mods necessary? How much do I gain in quality if I do the BNC mod, C31 mod and 40Mhz crystal mod?
2 – Can I somehow sync audio without (drift) issues without clockgen mod from RF audio capture or should I just capture only RF video and use audio track from conventional capture?
3 – Is there any point capturing head switch singnal with third capture card?
4 – Do I need a expensive & hard-to-find CRT monitor to check tracking or can it be done in some other way?
5 - There seems to be some new USB RF hardware in development, will it be worth the wait aka considerable upgrade to CX cards?

Oh, one more, don't laugh at this, I haven't touched a VCR in 20 years: I have some "non-important/whatever/dontcare" tapes which I'd like to capture but I'd also like to keep them recordable by not breaking the tab, can I trust my VCR & VCR operator skills to not record over them in capture process? (I said, don't laugh!)

Thanks in advance.

1. Direct Head Amp tapping is the most direct so the most signal potential, however some decks don't play nice with it due to the signal draw, very much so if your not using an impedence matched amplifyer, but how drastic this diffrance is between the test points and the head amp directly thats a deck to deck basis situation and anyone who say's diffrent is talking about a single deck or single line-up with same exact RF path internal hardware or just has no clue.

2. Yes, you can use probes but it has worse electical potential and is less secure signal and ground connection, your touching metal instead of welded to it.

3. You can solder or use DuPont cables, personally as my taps go to bulkheads I just solder its not going anyware and its the same known quality RGxxx cable.

(But this does not mean ignore the potential of the headers solder joints being weak or cracked, alongside any of the drum path always reflow these joints and paths to ensure a solid connection, even serviced decks people don't check and reflow all the joints inside the connectors for head amplifyers and this has a massive diffrance in SNR and does not affect standard untill in a really bad state, pre-emptive maintenance matters! this is why lower end modern decks with less parts and joints can have less issues lol)

4. Yes, they are diffrent signals one is baseband (Linear) either stereo on pro decks or mono on consumer decks, and one is FM modulated and this is HiFi, but for context baseband is the same as whats comming out of the back of the deck so you can always add a RCA or two for dubble mono linear when there is also HiFi on the tape, but some decks may disable the Linear audio feed when there is HiFi present.

5. The ADA4857 amplifyer is the go to standard now and should be deployed if possible so your bulkheads on your tapped deck are pre-amplifyed and impedence matched at the input end and the outbound end for your capture device.

(For example @20nicholasserra used a DdD at way too low gain level, that results in a poor capture and not the full potential of the signal being saved, the decoders can only work magic if there is signal to work with in the first place.)

Now the Black SNR vlaue is a rough outline of the real signal to noise ratio of course 44-50dB is golden range but most VHS tapes will only be around 38-44 dB max for Video8 I have seen 45-50dB on 1990s and 2000s tapes, but visually human inspection wise can be more accurate then the sampled lines for bSNR as its not based off the entire signal frame and is affected by dropouts from the tape.

6. No diffrance, just adding a BNC bulkhead for CVBS Output and or Input is handy and a cheep upgrade from crappy adapters or adaper cables if you have a pro monitor or kit with BNC cables it saves using RCA cables and is snag proof compared to RCA.

I will note I like HORSA cables, but I think things like BlueJeens are well a bit of a scam when users are not even going over and reflowing solder joints on the RCA connectors that the cables connect to in the first place to ensure a solid signal path.


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1. They are easy and improve RF level SNR, you want as much as you can get out of these, now the RCA mod is perosnal but C31 is an always at this point.

2. Why do you think we have the clockgen mod? it was 100% built to remove this issue and it also came with more benfits like software setting the hardware crystal rate, and baseband audio capture added with it on that same clock, this also neatly is 1 command capture with scripts or vhs-capture-server now.

(if you cant afford it, yes of course you can do everything 100% manual with a refrance capture thats how everything prior was done, but hardware sync + audio audio align saves hours of effort and is a more technically correct capture and archival workflow.)

But yes the C31 mod is a 100% always do it thing now.

3. Just to clarify for readers NO we don't capture headswich with a 3rd CX Card. We have a input on the Pi Pico do it with the clockgen mod and its light version even, adding it to the audio file.

(Its a useful bit of archive refrance data but not used with current software decoding, but can and might be used later so its worth the few extra MB of space archive wise.)

4. You don't 100% need a PVM or BVM CRT hell anyone will tell you an easycrap can do but a GV2-USB is a hell of a lot better for view/refrance of runtime/sync but any basic consumer CRT to view the live feed unaltered is always the best way to monitor analog captures, as you will catch SNR shifts and headcloging very fast. (If you CAN get a broadcast style unit I would, they are very nice and well built mostly and have H/V shift to see the VBI space)

5. The MIRSC is on rev V2.1 with 4ch audio built-in and is a working device, however its not got a finalised data interface and capture app, as the FX3 is a pain in the ass to work with. So today I would stick to the clockgen mod which with the new amplifyers is more then aduquite for colour-under formats for archival grade captures and total setup is sub 120USD with cards + tooling and the new ADA amp.


PS: Just remove or disable the decks record button easy idiot proofing or put a box latch on it or disable the erase head and or record paths lots of ways to go abouts this, but always good to have broken tab test tapes, if anything cheep commerical release tapes (spiderman is used a lot for the NTSC folk) are sort of the go to standard.