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Old 6th October 2014, 15:13   #1  |  Link
SpOeK!
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S-Video performs worse than Composite

Hi!

I'm trying to convert some old VHS-C tapes with an old AverTV card (M168-U) and a VCR. After doing some successful tests with the composite input I moved to use the S-Video input but with worse results than the former.

Here are two images captured using both inputs:

Composite
Name:  composite.jpg
Views: 1455
Size:  35.0 KB

S-Video
Name:  s-video.jpg
Views: 1449
Size:  72.8 KB

As you can see, the S-Video image has a lot of noise? interferences? and seems to have worse quality than the supposedly inferior Composite.

I've been looking for more information and I found this thread in AVforums. To me, it seems the same issue but none of the suggested fixes was useful.

I've tested the cable with the TV and I can't see the noise so the cable and the VCR are OK. All of this with the PC running trying to see if sharing the plug was a problem. Besides, even with no tape inside the VCR and using different VCRs I'm able to see that noise in the PC. On the other hand, the composite input works flawlessly always. Moving the PC or the VCR to a different grounded wall plug was useless. Using the official drivers or btwincap and different DirectShow apps makes no difference.

Is my AverTV card broken? Bad shielded? Any suggestions or ideas?

Thank you for your time.
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Old 6th October 2014, 15:24   #2  |  Link
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If the s-video output of the source is ok (remember that only S-VHS has S-video (there is a single exception, out of millions of models), so any device that gets S-video out of a VHS deck actually tricks the capture), then it may be that either the cable is broken (one reason why S-video never made it to the studios) or the filters (which may be as little as ferrite pearls) are defective/bad/too aggressive.

There are lots of devices that yielded a better image with composite rather than with S-Video, in particular at conversions.
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Old 6th October 2014, 16:43   #3  |  Link
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i can't see the pics
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Old 6th October 2014, 16:47   #4  |  Link
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My VCR is not a S-VHS but why I'm getting a nice picture using S-Video without any noise or interferences in the TV but not in the PC. That would discard a bad cable (TV image is OK).

I'm using a SCART to S-Video cable (like this) to connect the VCR to the PC but when I'm testing the VCR with the TV I need to add a converter (like this) from S-Video to SCART (no S-Video input in my TV). So here's my theory:

According to Wikipedia, the S-Video Y pin is shared with the Composite pin while the S-Video C uses a different pin and is not shared with the Composite (picture OK). So my guess is that the TV is unaware that the input is S-Video and is running in, let's say, Composite mode. The PC is pretty aware that the input is (should be) S-Video and is trying to use the two signals but S-Video C pin is carrying garbage (is a regular VHS not a S-VHS).

Does it make sense?
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Old 6th October 2014, 16:54   #5  |  Link
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Quote:
Originally Posted by Mounir View Post
i can't see the pics
I'm sorry. It says "Attachments pending approval".

I've uploaded them also to imgur.

Composite


S-Video
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Old 6th October 2014, 19:43   #6  |  Link
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Something is terribly wrong with the S-video input on your PC.
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Old 6th October 2014, 20:28   #7  |  Link
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I doubt it. I believe that's exactly what you would expect to get by feeding a composite signal into S-Video input, which is what he's doing with that SCART adapter from a regular VHS deck.

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Originally Posted by SpOeK! View Post
My VCR is not a S-VHS

...

So my guess is that the TV is unaware that the input is S-Video and is running in, let's say, Composite mode. The PC is pretty aware that the input is (should be) S-Video and is trying to use the two signals but S-Video C pin is carrying garbage (is a regular VHS not a S-VHS).
Sounds right to me, except that the C pin isn't carrying "garbage" but rather a second copy of the composite signal which is being ignored by the TV and incorrectly used by the capture card.
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Old 7th October 2014, 00:29   #8  |  Link
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Of course you are correct, that is what I get for reading the first post and skimming the rest. I usually don't do that.

For a non S-VHS VCR composite is the way to go. ChiDragon got it.
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Old 7th October 2014, 07:56   #9  |  Link
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Now that is exactly as I supposed, I join the others that were faster than me.
A TV is very tolerant with input signals, and usually picks up the best choice when a signal is input. Remember that TVs are also insensitive to Macrovision

What you have there is the bleeding of chroma into luma.
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Old 7th October 2014, 10:56   #10  |  Link
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Thank you all for your answers. You were right.

Certainly, I read in several places that only S-VHS decks offered S-Video outputs but I was hoping that all that info was a bit outdated and that recent or, at least, some of the latest regular VHS decks sold in the market were offering this type of signal through the SCART output. And then I gave a shot to the SCART to S-Video cable and saw an almost working signal and I thought: "Well, it seems that the S-Video output in this deck is working. Probably the cable or the card are low quality and that's why I'm getting all that noise."

But no, I was deluding myself due to my poor understanding of what were really going on in the SCART output.

As a final test, I have a DVD player with a S-Video output and using a S-Video cable I'm able to see a clear picture in my PC. Even more, I've been able to test the VCR and the SCART to S-Video in a TV with an actual S-Video input and the image is as bad as in my PC.

All of this confirms what you said. Case closed.

It's time for me to decide if I sticks with the Composite output or if I should try to get a S-VHS deck.
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Old 7th October 2014, 14:15   #11  |  Link
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Quote:
Originally Posted by Ghitulescu View Post
If the s-video output of the source is ok (remember that only S-VHS has S-video (there is a single exception, out of millions of models), so any device that gets S-video out of a VHS deck actually tricks the capture), then it may be that either the cable is broken (one reason why S-video never made it to the studios) or the filters (which may be as little as ferrite pearls) are defective/bad/too aggressive.

There are lots of devices that yielded a better image with composite rather than with S-Video, in particular at conversions.
Guys, most of VCR's (if not all of them) record chroma in separate part of spectrum - they can have S-Video (or rather separate Y and C output) by physical construction of signal path.
S-Video connector appear together with S-VHS - as it was requirement to further improve video quality but there is nothing against to have S-Video in non S-VHS VCR.
In fact everyone can modify already own VCR without S-Video and add S-Video output.

Feeding CVBS to S-Video mean for capture card only that card doesn't try to separate chroma and luminance (this can be performed on many ways) - in fact luminance and chrominance separation can be performed in software way better than internal capture HW method.
http://www.jim-easterbrook.me.uk/pal/ - thread about software TBC partially cover this aspect - Bt878 and compatible cards can be programmed to capture 4*Fsc video as grayscale with H-sync and burst - rest of processing can be done in software even offline.

Side info - this is purely theoretical as real VHS have limited bandwidth and in many situations chroma and luma occupy CVBS in non overlapping way (Y bandwidth is usually well bellow 3.2MHz where chrominance carrier is 4.43 and bandwidth for U&V is around .5MHz ie 4.43 +-.5Mhz - but even with full chrominance legal bandwidth i.e. 1.25 - 1.5Mhz they should be quasi non overlapping for ordinary VHS as 4.43 +-1.5MHz is in worse case scenario 2.93Mhz for Y).

Last edited by pandy; 7th October 2014 at 14:27.
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Old 8th October 2014, 16:24   #12  |  Link
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In fact everyone can modify already own VCR without S-Video and add S-Video output.
I eagerly await your step-by-step instructions for how to modify each of my VHS machines. (Not sarcasm.) All I know is that there are "test points" and soldering involved.
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Old 8th October 2014, 17:06   #13  |  Link
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Quote:
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Guys, most of VCR's (if not all of them) record chroma in separate part of spectrum - they can have S-Video (or rather separate Y and C output) by physical construction of signal path.
I know that and I suppose other people know that as well.

The point is different. Even after S-VHS appeared and established a market for S-Video (like cables, terminals like projectors, mixers etc), S-Video was not, by purpose, introduced into VHS gear.

Surely, one can inject or extract Y and C in and from various part of the electronics, yet this is far from what Average Joe can do.
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Old 9th October 2014, 12:14   #14  |  Link
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I eagerly await your step-by-step instructions for how to modify each of my VHS machines. (Not sarcasm.) All I know is that there are "test points" and soldering involved.
Provide list of machines - better service manual for each of them (are you vaporeon800?).

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I know that and I suppose other people know that as well.

The point is different. Even after S-VHS appeared and established a market for S-Video (like cables, terminals like projectors, mixers etc), S-Video was not, by purpose, introduced into VHS gear.

Surely, one can inject or extract Y and C in and from various part of the electronics, yet this is far from what Average Joe can do.
Explanation

I stand on position that Science is neutral - if someone asking me how to make explosive then i'm not trying to censor this kind of information to prevent imaginary danger.

That's why i saying that Y&C are available separately in VCR thus they can't be presented as unique only for S-Video (and S-VHS like VCR's). Hope it is clear now.
(and as VCR capturing seem to be hobby for many of us (average Joe's) then i see no reason to not modify already owned VCR to provide separate Y & C).

Last edited by pandy; 9th October 2014 at 12:22.
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Old 9th October 2014, 15:24   #15  |  Link
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The point was that many Joes (plural of Joe) could not distinguish S-VHS from VHS on their average TVs. Surely a big screen TV would have been needed for the S in S-VHS .

So the presence of S-Video was used as a marketing instrument to promote S-VHS over VHS.
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Old 9th October 2014, 16:49   #16  |  Link
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The point was that many Joes (plural of Joe)
As i explained many times - my English is self learned and full of mistakes (formally i've learned English for approx 5 months).
Sorry.

Quote:
Originally Posted by Ghitulescu View Post
could not distinguish S-VHS from VHS on their average TVs. Surely a big screen TV would have been needed for the S in S-VHS .

So the presence of S-Video was used as a marketing instrument to promote S-VHS over VHS.
I hope that most of people on this forum are able to distinguish between VHS and SVHS and DVD.
And i agree - S-Video connector was marketed as integral part of SVHS system but this is plain marketing.
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Old 11th October 2014, 03:36   #17  |  Link
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Provide list of machines
Answer to your question: yes.

Partial list:
Magnavox VR9960AT01
Sony SLV-585HF
Sony SLV-779HF
Sharp VC-H9888U
Panasonic PV-V4524S
JVC HR-J693U
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Old 12th October 2014, 09:16   #18  |  Link
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Quote:
Originally Posted by pandy View Post
I hope that most of people on this forum are able to distinguish between VHS and SVHS and DVD.
And i agree - S-Video connector was marketed as integral part of SVHS system but this is plain marketing.
Well, this discussion went away from its original intended purpose.

When I said that VHS-gear doesn't have S-Video (although it records as Y/C) I did it to explain the OP that whatever he has done it was wrong, and the capturing card told this to him .

Now, S-Video was kept for S-VHS (and Hi8) due to marketing reasons. I agree that probably most people here can recognize VHS from S-VHS and from DVD, yet the marketing addressed the rest of 7 billion people . S-VHS and VHS are indistinguishable on a TV of the '80ies, when it appeared, surely many people will tell them apart today on a 60" flatscreen. Our eyes also learned how to get the finest details, we learned this from Blu-ray. The audience of Edison's early 1900 phonogram demonstration couldn't it tell apart from a live orchester in a blind listening. Which is lame by today standards . That was my point - masses and technology pinponted in time.
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Old 13th October 2014, 13:56   #19  |  Link
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Quote:
Originally Posted by ChiDragon View Post
Partial list:
Magnavox VR9960AT01
Sony SLV-585HF
Sony SLV-779HF
Sharp VC-H9888U
Panasonic PV-V4524S
JVC HR-J693U
As this is way more than OT please create new thread for this.

At first i was able to download service manual for Sharp VC-H9888U - Y signal is available at pin 52 IC201 (IC201 HA8311AF - no datasheet is available on internet - as usual in case of Japanese custom electronic) and on connector P208 (pin 1), C signal is available at pin 55 IC201 and on connector P209 (pin 2).
Based on block diagram those signals are combined in circuitry (part of Gamma Circuitry) made from Q551, Q552, Q271, Q272, Q274 to create CVBS.
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Old 13th October 2014, 17:07   #20  |  Link
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One of the VCR that I'm using it's a Funai 25A-750. Following the same idea of finding the logic in charge of the Y/C mix and maybe intercepting the signals before this mix was carried on I've been able to get the service manual.

I've located the IC301 (LA71750EM) in charge of all these tasks. One pin (25) seems to carry "PB C OUT (Playback Chroma out?)" but sadly I still haven't found a similar pin for the Luminance. Best chance right now is pin 46 which is dubbed VCA-OUT but I'm just guessing without the proper datasheet.
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