S-VHS Internals


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S-VHS Internals

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retrofan
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Jan 20, 2010, 2:21 AM

Post #1 of 10 (3596 views)
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S-VHS Internals	Can't Post

Hello,
I just wanted to know a very obscure question. How is the video stored in S-VHS tapes? Is the chroma kept physically separate from luma? To me, this would seem to require a separate track on the tape for chroma or some other way to keep it separate.
I know that, in laserdisc, the signal was stored as composite and even ones with svideo connectors, simply applied the composite to a comb filter to create a pseudo-svideo signal. This is why I distrust any answer which says "S-VHS VCR's have svideo connectors, therefore the signal was stored separately.". No way, no guarantee at all.
HI8 always uses a similar system as S-VHS, so if you know about that one as well, let me know.
Thanks.

jts1957
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Jan 20, 2010, 4:15 AM

Post #2 of 10 (3594 views)
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Re: [retrofan] S-VHS Internals [In reply to]	Can't Post

http://en.wikipedia.org/wiki/Videotape

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retrofan
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Jan 20, 2010, 7:59 AM

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Thanks,
however, the answer was not in the article provided. My main question is, does SVHS store color and luma separately internally, and how does it do it.

jts1957
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Jan 20, 2010, 11:03 AM

Post #4 of 10 (3588 views)
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Re: [retrofan] S-VHS Internals [In reply to]	Can't Post

Since you couldn't be bothered to click on S-VHS links in the 1st article, try:
http://en.wikipedia.org/wiki/S-VHS

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retrofan
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Jan 20, 2010, 8:10 PM

Post #5 of 10 (3582 views)
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Re: [jts1957] S-VHS Internals [In reply to]	Can't Post

Hello,
Sorry for the confusion. I read that article as well. The only reference it makes is "Like VHS, the S-VHS format uses a "color under" modulation scheme." With no further explanation, I don't know what this means.
The article on modulation is too general, and doesn't explain the VHS method.
It's still possible, that both (even VHS) store the color separately, and yet only S-VHS bothered to provide a connector to take advantage of it.

jts1957
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Jan 20, 2010, 9:57 PM

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http://en.wikipedia.org/wiki/Heterodyne

You really should try google, it's wonderful! Smile

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(This post was edited by jts1957 on Jan 20, 2010, 9:58 PM)

retrofan
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Jan 21, 2010, 1:58 AM

Post #7 of 10 (3575 views)
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Re: [jts1957] S-VHS Internals [In reply to]	Can't Post

Ahh, heterodyne I know, that's just multiplying two signals which gives the sum and difference. However, this must be heterodyned again, since the carrier for S-VHS is 5.8MHz.
So a color carrier of 629KHz is used instead of ~3.58. Instead of pinstripe suites being mistaken for color, anything in the range of 40 cycles/line is now mistaken.
(629KHz color carrier/15.75KHz line frequency=40 cycles/line. 40 c/l*3/4 (lines/picture height)=30 lines resolution (standard analog video resolution measurement).

Interesting, I've recorded that frequency and didn't see any rainbow effects. The video for both VHS and S-VHS, swept in frequency, are on my webpage.
http://code.google.com/p/avisynthrestoration/wiki/Testpatterns

You'd need a new kind of comb filter to separate chroma/luma better when taken from an s-video connector. I could write a software filter for that!

You've given me a lot to think about, thanks! (I did try Google, just not using the right search terms).

retrofan
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Jan 22, 2010, 5:03 PM

Post #8 of 10 (3566 views)
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I finally found a good explanation
http://catalogs.infocommiq.com/AVCAT/images/documents/pdfs/TT189%20-%204611.pdf

The chroma is separate in all VCR systems, obviously only those with an s-video in connector can record a source already separated.
The color resolution is exactly the same in vhs, beta, umatic, hi8, and supervhs. Only luminence bandwidth varies.

denonjapan
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Jan 29, 2010, 5:38 AM

Post #9 of 10 (3555 views)
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Re: [retrofan] S-VHS Internals [In reply to]	Can't Post

HAHAHAHHAHAHAHHAAAAAAAAAAAAA...........Why bother to asked these now? it's absolete.........your funny!

denonjapan
made in japan

jts1957
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Jan 29, 2010, 7:10 PM

Post #10 of 10 (3541 views)
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Re: [denonjapan] S-VHS Internals [In reply to]	Can't Post

I like Obsolut Vodka. Unimpressed

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