Particular S-Video vs. Composite Question

[Anonymous4]

12

[edDV]

S-VHS records to tape with separate Y/C components. S-Video keeps the components separate through playback and export.

I see no rational reason to combine Y and C to composite only to separate them again in the ADVC. Y/C separation is a lossy process.

[Anonymous4]

12

[edDV]

Sorry. I should have mentioned that my source tape is not an SVHS. The source tape is regular VHS.

VHS is also recorded Y/C but Y is low pass filtered to 3MHz before recording. If you export Y+C composite you are adding noise to Y above 3MHz. Again no advantage to composite. With normal VHS players, composite is the only option.

[Anonymous4]

12

[edDV]

VHS, S-VHS, Video8, Hi8 and U-Matic are all recorded "color under". Chroma is stripped off and down converted below ~500KHz.

Only broadcast formats (e.g. 2" Quad, 1" Type B/C, D2, etc) record Y+C composite.

Component digital formats record YCbCr.

[Anonymous4]

12

[edDV]

OK

So here is a thought experiment to see if I actually know what's going on.

So a given VCR has a 3DYC comb filter.

If a composite signal is sent into the unit, the 3DYC comb filter splits it into Y & C and records those separate signals to the VHS.

Yes. For VHS the Y is low pass filtered to 3MHz. For S-VHS Y extends to ~4.5MHz giving more luminance detail.

If an S-Video signal is sent into the unit, the 3DYC comb filter is not used and the already separate Y & C signals are recorded separately to the VHS.

Yes.

Now in playback, using the S-Video output (or composite I suppose), the 3DYC comb filter doesn't come into play correct? It's only active on an incoming signal right?

Correct. For-S Video out Y and upconverted* C are sent separately.
For composite out, Y and upconverted* C are added to make composite.

Originally, I supposed that a composite signal was recorded onto the VHS tape. The 3DYC comb filter would then activate when reading the VHS tape and separating the signal to send over S-Video connections. Writing this out now sort of seems like a huge supposition.

The recorder comb filter works on the input side as you said. If composite is sent to the next capture device, Y/C separation is done there.


* Chroma is down converted to ~500KHz for recording. On playback the chroma is remodulated around a 3.58MHz subcarrier to make C.

This is the best diagram Google could find (Portuguese) of color under FM S-VHS recording. VHS would have Y limited to 3MHz max.
Cor/C = Color under
fc = color subcarrier (3.58MHz for NTSC)

http://www.broadcastbuyersguide.com/bbg/editorial/features/edit_2/4

[Anonymous4]

12

[ntscuser]

It was a little publicised feature of S-VHS machines that they could also playback prerecorded standard VHS titles in superior quality to composite video via the S-video output. I used to watch all my sell-thru tapes that way. Domestic VHS machines could also have been fitted with S-video output sockets but for various marketing reasons never were.

[SatStorm]

Let me testify something here:
I have a VCR with S-Video out. It is a SVHS from Philips, a nice one, with linear TBC and some other build in filters.

When I use S-Video out, my Toshiba X27 standalone DVD recorder, can't record the chroma of some - not all - SECAM tapes, taped back in the early 80s.
If I use Composite, I have colour on TV but again no colour on the DVD Standalone!

Anyway, I end up using more composite for SECAM than S-Video. Am I do it right?

[orsetto]

Theory and ideal circumstances are one thing, practical realities with the typical so-so standard VHS tape is another. My experience with PC encoding is limited, but I've spent years slowly transfering my huge VHS library to an assortment of DVD recorders. I've found (with my tapes anyway) that the SVHS vcr output is not always necessarily better than composite. DVD recorders can be peculiar beasties, reacting in unexpected ways. In my work, I've found it runs about 50/50 whether the transfer looks better coming off the vcr's SVHS or composite tap. An actual SVHS recording almost always benefits from the SVHS connection, pre-rec Hollywood VHS usually looks better via SVHS output, but off-air and especially cable-sourced regular-VHS recordings differ tape to tape: many show a terrible increase in noise over the S-video connection. The composite sacrifices detail for more watchable smoothness. To some degree the specific VCR is a factor: my AG1980 does better on S-video out than my AG1970, my JVCs are all over the place and unpredictable, and my Mitsubishi DVHS is almost always better thru S-video, especially if its DNR/TBC is active. Once a tape drops below a certain "quality threshold", all bets are off: anything second-generation or slower than SP has to be tested on all the VCRs and their outputs until I hit the sweet spot. More often than not my poorest tapes will play much better on a common VCR over composite than on a deluxe SVHS vcr with TBC and S-out.

I guess what I'm saying is it pays to check each tape over both S-out and composite, if you have a wide variety of tape types and you're really picky about results. Most people who aren't totally anal can probably standardize on just one typical connection: the differences are often too subtle to be bothered fussing too much over and it does increase the workload appreciably for a sometimes-modest shift in quality.

[lordsmurf]

s-video is a transmission/wire type, S-VHS is a tape format
Not the same.