WTB: Time Base Corrector for S-VHS

[TerraHertz]

Hello Terrahertz, welcome to the discussion! You can see an example of the issue I am facing on the previous page: Chroma Issue Example
If you don't see it, I can send you the frame via mp.

Ah, I see it now. Turns out there is *also* a problem developing with images on this forum (ironic), in that suddenly some don't display in my usual browser (Opera, pre-chrome). But it does display in Firefox.

Anyway, yep, that's definitely a chroma-lock failure problem. The saturation suggests the color burst amplitude is too low. This results in poor lock, but ALSO color decoders often use the burst level for gain control. So, low burst, causes any color in the image to be super saturated.

Do you have your monitor set to underscan? Ha, silly me, that's an image from your capture device, not the monitor. So of course it grabs a little more than the standard frame area.
There's a head switching horizontal tear near the bottom. Is that stationary? Is that a paused image, or capture from a normal speed playback?

Now, my preliminary defect analysis:

• I have no horizontal/vertical jitter at all, so this leads me to think that the luma sync signal (i.e. line and frame sync) is OK.

Yes, looks OK to me. Vertical edge of the bottle is straight.

[/li][li] In fact, if I try removing the color after capturing the video, I obtain a nice and clean B/W video, with no noticeable defects. Just the chroma is really tremendous.
[/li][/list]

During my search I found this piece of information, which gave me a lot to think about:

The two major problems are incorrect sync and burst levels that causes increases or decreases in luminance and chroma levels that get worse down the line. Specifically, video recorders. Images get brighter or darker, color levels get higher or lower. Usually the chroma winds up going through the roof because of the poor frequency response of consumer recorders, causing increases in color levels.

Source: VideoHelp Forum, post #13 by videobruce.
I can't figure out how the supposedly limited bandwidth of consumer recorders can affect chroma so much. Yes, the chroma burst from the VHS looked a bit weak if compared to the robust signal provided by the camera, but can this really make so much difference?

Sure can! The burst level, duration, shape etc are supposed to be constant and standard. The level in particular is used as a reference for gain control. TVs/monitors tend to be very forgiving.

If this is the root cause, I guess that TBC is the way to go: rebuilding the chroma burst may solve the issue.

Assuming the TBC input can work with such a bad signal. It may not, the TBC is supposed to be for fixing timing errors and horizontal bar dropouts due to fast or slow play  tracking. Not so much for fixing broken signals.

Before proceeding, I would like to collect your opinions. TerraHertz, if you think a video analyzer could help, let's follow that road! Do you have something to suggest?

I don't think you mentioned which video system you're using? PAL, NTSC or SECAM?  (Online lists say Italy used PAL VHS.)
Also if you mentioned having tried multiple video cassette players, or just the one?
And is it the same for all tapes you tried?
And have you tried playing some random tapes from other sources?
For hunting this problem, best to get some worthless tapes that produce the same effect, so you're not playing the precious tapes over and over. There is wear, and always the chance of a machine chewing the tape. Especially an old machine. Btw, if your tapes are precious, NEVER pause the image. The head then runs over and over the same spot on the tape. Not good.

Can't you find another VCR you can borrow to try? That would be my next.
If not, have you tried cleaning the VCR heads?

Should I get a video analyzer before, and then choose the right TBC?

I think first you should see if your VCR is mangling the color burst off the tape, or if the tapes are old/bad.
Google pal video waveform standard
You'll find plenty of info on what the waveform should look like.  eg https://www.maximintegrated.com/en/app-notes/index.mvp/id/734
The burst pp level should be the same amplitude as the sync-tip to back porch (where the burst centerline sits.) For 1Vpp video that's 0.3Vpp.

You can do that with a scope, no need to get fancy.
I don't know what the used video test gear market is like in Italy. Something like this:
http://www.ebay.com/itm/TEKTRONIX-1735-1725-PAL-NTSC-VECTORSCOPE-WAVEFORM-MONITORS-DUAL-CASE-/351509643320?hash=item51d79b8038
would do what you need, but vectorscopes do require you understand what you're doing. Heh. that one is listed as 'vectorscope no signal', but it's possible they don't know how to operate it.
Probably not worth getting such a thing for your problem, since it's likely simple - a bad VCR.

[aargee]

I still reckon a professional VCR like the AG 7350 would be a good start, although I'd beg or borrow one from somewhere first to see if it makes a difference.
My 7350 had no problems with commercial macrovision correction and other weird problems associated with old de-generating tapes. The output S-Vid signal was fed through a DV-Cam to produce a firewire signal then into a 2009 Mac.

[Richard Crowley]

How many tapes are you trying to capture?  How important is this?

At this late date in the life-cycle of VHS, it may be the better part of valor to simply turn the tapes over to a professional to transfer/capture.

Unless you want to get into the business of capturing old VHS tapes and become an expert yourself.
Perhaps that is a viable business model that is in demand in your part of the world.
But otherwise, it just seems like a tremendous amount of time, money and effort for such modest result.

I would NOT recommend that TBC-4000 unless you can PROVE that it can function on PAL (assuming you have PAL tapes).
The AVT-8710 looks far more promising from the description.
It seems quite remarkable that similar used gear isn't available in the EC???  Why is that?

[brabus]

Having identified the issue in the chain is a remarkable success. Thanks a lot to you all, I really learned a lot in this discussion!
I think you all deserve some answers, so let me proceed chronologically:

(...)
You have not revealed any background about these tapes. The more you know about them, the better chance you have of devising a scheme for replaying them successfully.  For example, do you know who, when, how, they were recorded?  Do you possibly have access to the machine they were recorded on?  The "calibration" between the recording machine and the playback machine is called "interchange". They tried to maintain some level of interchange to allow tapes to be played back on other machines properly.  And parts of the interchange problem would exhibit as time-base errors upon playback.
(...)

I have access to the video camera used to record the original tapes, but then the VHS-C tapes were transferred to normal VHS' using a Sanyo VHR-290 VCR, long time gone. Playing them back with the Metz 9877 adds a third device in the chain, explaining the final degradation of chroma, although Luma and sync are intact. So in the end: one ring in the chain is missing.

(...)
I have a new Sensoray 611 card (bulk) here but I've never used it and I don't have any analog video sources either, so it's essentially for sale.

Thanks a lot for your offer, but I think I will keep my ADVC-55 and add the right block in the chain, between the VCR and the '55.

(...)
Anyway, yep, that's definitely a chroma-lock failure problem. The saturation suggests the color burst amplitude is too low. This results in poor lock, but ALSO color decoders often use the burst level for gain control. So, low burst, causes any color in the image to be super saturated.
(...)

I think this is the most convincing analysis, but:

(...)

If this is the root cause, I guess that TBC is the way to go: rebuilding the chroma burst may solve the issue.

Assuming the TBC input can work with such a bad signal. It may not, the TBC is supposed to be for fixing timing errors and horizontal bar dropouts due to fast or slow play  tracking. Not so much for fixing broken signals.
(...)

I also guess that the AGC of the TBC will reproduce the same mess I see on my screen. I definitely need a TBC with an adjustable chroma gain.

I don't think you mentioned which video system you're using? PAL, NTSC or SECAM?  (Online lists say Italy used PAL VHS.)

PAL

Also if you mentioned having tried multiple video cassette players, or just the one?

I have a Metz 9877 and a Panasonic NV-F65 (actually I had two of them, one just sold; results were the same).

And is it the same for all tapes you tried?

No, some tapes play better than the others, but I observe a general chroma saturation. I have some of the original VHS-C tapes (24 years old!), they play noticeably better than the VHS in which the content was copied; I use a VHS-C to VHS adaptor. Shame I only have 10 original VHS-C (5 hours total), against ~20 VHS varying from 120 to 240 minutes. My father used to transfer the content of the VHS-C to normal VHS.

And have you tried playing some random tapes from other sources?

Unfortunately I don't have other tapes, but I'll try finding out something to use as a reference. I will try to record something on a blank VHS and play it back using the same VCR, I am pretty sure the result will be flawless.

Btw, if your tapes are precious, NEVER pause the image. The head then runs over and over the same spot on the tape. Not good.

You are right. I did it a couple of times, promising to myself not to do it again.
Some people advice to run the tapes full forward and full reverse a couple of times before playing them; I don't understand why this could bring any good, but I can assure that some tapes play better when they are played for the second time. Electrostatic charge to dissipate?

Can't you find another VCR you can borrow to try? That would be my next.
If not, have you tried cleaning the VCR heads?

I will try to find another VCR, but I am starting to be pretty convinced that the origin of my issues lay in the long signal chain between the first record and the final play. The missing Sanyo VHR-290 could have played an important role.

The burst pp level should be the same amplitude as the sync-tip to back porch (where the burst centerline sits.) For 1Vpp video that's 0.3Vpp.
You can do that with a scope, no need to get fancy.

I already analyzed the signal with the scope, noticing a quite big difference in amplitude between the burst and the color signals. If I was an AGC, I would wind up to max gain.
I thoroughly cleaned the heads with isopropyl and hard cotton sticks, always applying mild tangential force to the heads and drum, in order to avoid breaking/misaligning them. I removed some dirt, but nothing serious. The VCR seems having seen not many cassettes.

Probably not worth getting such a thing for your problem, since it's likely simple - a bad VCR.

I am really curious to try another VCR, although the two I already have play flawless on TV and behave in the same way with the capture devices.

How many tapes are you trying to capture?  How important is this?

About 10 VHS-C (30m each) and about 20 VHS (120 to 240 m each).

At this late date in the life-cycle of VHS, it may be the better part of valor to simply turn the tapes over to a professional to transfer/capture.
Unless you want to get into the business of capturing old VHS tapes and become an expert yourself.

That is a sensible advice; a reasonably professional service would cost me ~300€.
But I prefer to keep control over the final result, and spend more or less the same money in equipment and increase my knowledge.

Perhaps that is a viable business model that is in demand in your part of the world.
But otherwise, it just seems like a tremendous amount of time, money and effort for such modest result.

Actually, less and less people is transferring old tapes into DVDs, the majority of them already did it - in any case the market is very small, and you always end up discussing the quality and the price with the customer. Some professional services do it for 5€ (five Euro!) per cassette. Don't ask me about the quality, but for sure they get all the customers.

I would NOT recommend that TBC-4000 unless you can PROVE that it can function on PAL (assuming you have PAL tapes).

Good point. Meanwhile, I bought a small and cheap video processor with chroma/saturation/contrast adjustment capability; I just want to try reducing chroma level before feeding it to the capture device. If this fixes the problem, I can actually avoid a TBC.

The AVT-8710 looks far more promising from the description.

Noted. I still can't figure out the differences between the models. Perhaps the AVT is just the best seller, therefore the cheapest.

It seems quite remarkable that similar used gear isn't available in the EC???  Why is that?

Really, really good question. Even in Germany I can't find something interesting.
In general, US electronics market is by far better than EU.

[SL4P]

As you have decent H and V lock, as others have said - there are questions about subcarrier /chroma.
Many TVs will accept a witches brew of colour standards - some of which are non-standard...!

My thought is that the colour may be modulated in a PAL 3.58 subcarrier (rather than 4.43) - which would exhibit the symptoms you describe.
Some TVs will auto-switch, and display the video format info in the corner of the screen, or if you can find a loaner - try a 'standards converter' that understands PAL 3.58. 
(above comments written with the assumption you are in a PAL TV market!)

[brabus]

...and we have some new results!

Following the road of the chroma root cause, I decided to try a cheap analog video processor, just for the sake of it - actually to investigate the road without wasting too much money on it in case it was wrong.

I managed to obtain an old "Carena MVP-4000" for about 20€ (pictures).

Well, I kept the video level, contrast and sharpness unchanged, and just lowering the saturation I obtained the result in attachment. Heck, we can even read the "45" on the letter, meaning the 45th marriage anniversary of my grannies (long time gone  )

That's a full success!

So, I thank all of you again for helping me figuring out the problem!
Now I am seriosly thinking about a TBC with chroma correction capability, but on the other hand I am wondering if I will obtain any benefit at all. My tapes are really not bad in terms of sync/dropout/noise, so I may be happy with the result and save many hundreds of €€€.

I could buy the AVT-8710, use it for the bunch of tapes I need, and then sell it back on the bay. These things should keep their value reasonably well, what do you think?

[SL4P]

That's a pretty good screen shot from an old VHS tape!
Congratulations on your persistence paying off

[brabus]

Thank you SL4P!

...and I just won an ebay auction for an AVT-8710! I am pretty sure I will obtain a better B/W contrast and lower overall noise with that device, instead of the cheap-ass "Carena". The 8710 won my preference thanks to the integrated controls. I am pretty damn sure that the interiors are *exactly* the same between the aforementioned TBC devices. We'll see!

Results and teardown will follow...