DVI or HDMI vs. HD-SDI - AVS Forum
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post #1 of 96 Old 07-18-2006, 07:41 PM - Thread Starter
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What, if any, are the advantages of HD-SDI over DVI or HDMI? It's a current topic on the CRT forum, but it doesn't seem anyone really knows. This seems like the forum with most knowledgeable members on this subject.

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post #2 of 96 Old 07-18-2006, 08:08 PM
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Glimmie would be the man to step up and really hit this one out of the park.
There are probably others here that know the nuts & bolts as to why HD-SDI performs better.

The most telling point to me are the origins of what we are comparing. HD-SDI was developed by & for the broadcast & editing world with the primary goal being all out performance.

DVI & HDMI were hatched merely to implement content protection.

Also important to note that not all HD-SDI is equal so lets put down some ground rules as clearly defined by the SMPTE, the Society of Motion Picture and Television Engineers

SDI: SMPTE 259M, 270 MB/s (not in the HD equation)

HD-SDI: SMPTE 292M, 1.45 GB/s
Dual Link: SMPTE 372M, 2.23 GB/s (2 coax connections)
Single Link 3G SMPTE 424M, 2.97 Gbit/s

Advantages are low jitter & superior signal integrity as well as higher data rates.
Now who can step in & gives us the why & hows?

Note: 1080P60 Film requires a 2.97 Gbps data rate.

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post #3 of 96 Old 07-19-2006, 12:23 AM
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HD-SDI makes sense mainly if you have an external video processor with HD-SDI input. In that situation HD-SDI basically cannot be any worse than HDMI/DVI, because HD-SDI simply transports the video stream without doing any harm to it. With HDMI/DVI the quality of the signal very much depends on what the device is doing. There are some devices which claim to offer clean HDMI output without doing any harm to the signal. But honestly I'm not really trusting most manufacturers. Some examples:

(1) The Humax HD sat receivers in Europe ouput the 1080i50 fields flipped. As a result both Lumagen and iScan video processors fail to correctly deinterlace the signal. The Lumagen got a firmware update in the meanwhile with which you can flip the fields back to the correct order. The iScan does not offer that, so I have to use 720p output on my Humax HD receiver, which is noticably less sharp than a clean 1080i50 output would be.

(2) Many HDMI devices do not allow to output YCbCr color space. Instead they convert the YCbCr video stream coming from the MPEG/VC-1/H.264 decoder to RGB and output RGB. That's a bad idea when having a video processor, cause this ends up in rounding errors and the video processor can do the color space conversion better, anyway.

(3) The Toshiba HD-DVD player clips BTB and WTW over HDMI, I believe.

Basically with HDMI you're at the mercy of how well the devices' HDMI implementation is. With HD-SDI you're guaranteed to get the untampered with video stream out of the device.

Ah yes, and with HD-SDI there's no HDCP involved. So you get faster switching and no handshake problems.
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post #4 of 96 Old 07-19-2006, 10:55 AM - Thread Starter
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I have to admit I'm a bit a of cynic. And the worst kind. An uninformed, ignorant cynic. I've always used an HTPC to watch DVDs and HD component out on my HD DVR satellite receiver to watch HDTV. This works well with my CRT PJ, so I've never followed or paid any attention to any of this stuff. With HD DVD now a reality, it's becoming more important to me.

I understand that standard SDI is a big advantage for an SDI'd DVD player when you have a scaler with SDI input(s). On the other hand, HD DVD players, and satellite or cable receivers, already have digital outputs. So the question is, is the HDMI output good enough, or is it lacking and needs to be improved?

So maybe the manufacturers don't always implement HDMI properly. That makes that particular gear bad, not HDMI. Lets assume for this discussion let's assume that HDMI is implemented properly.

Bandwidth: A 6' sewer pipe can move a lot more water than a 3/4" garden hose. But when all you have to move is 10 gallons an hour, a drinking straw will easily handle the job. Anything else is overkill with no gains or benefits. Does HDMI have enough bandwidth to handle what we use it for in an HT environment?

HDCP: Even us CRT owners can get around HDCP these days, so as far as blocking usage, it's not an issue--at least I don't think it is. Tell if I'm wrong. Does the presence of HDCP interfere with or degrade the picture quality? If not, eliminating it doesn't really accomplish anything.

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post #5 of 96 Old 07-19-2006, 11:50 AM
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I believe HDMI could theoretically offer equal image quality compared to SDI. But in real life it more often than not doesn't.
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post #6 of 96 Old 07-19-2006, 12:38 PM
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My Canon HD Camcorder has HD SDI outputs. It's very good and supports uncompressed 4-2-2 signals.

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post #7 of 96 Old 07-19-2006, 01:12 PM
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SMPTE 424M is capable of 4:4:4

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post #8 of 96 Old 07-19-2006, 01:29 PM
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post #9 of 96 Old 07-19-2006, 01:48 PM - Thread Starter
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I've seen that thread. That's about SDI. I started this thread specifically to address HD-SDI. Other than bandwidth, are they the same?

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post #10 of 96 Old 07-19-2006, 11:58 PM
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HD-SDI is quite different to SDI in how the data is transported. But in the end that doesn't matter. What is important is that both SDI and HD-SDI mods will transport the decoded video stream to the video processor, before the (H)DVD player can do any harm to it. So basically what is being said about SDI should also be true for HD-SDI.
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post #11 of 96 Old 07-20-2006, 12:58 AM
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Unless govey gets involved it wont stick. govey sux.

"Human's aren't the only species on Earth, We just act like it...."
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post #12 of 96 Old 07-20-2006, 10:11 AM
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Quote:
Originally Posted by madshi View Post

HD-SDI is quite different to SDI in how the data is transported. .

What are you saying is different assuming SMPTE292? Yes the ancillary data areas are a bit different but it's still 10bit Y and 10bit pBpR in a 4:2:2 cadence. Yes the clock rate is higher. HDSDI also uses the same NRZI scrambling algorithm as SDI. The electrical interface is also identical, 800mvpp across 75ohms. In fact they are so similar that modern chip sets do both SDI and HD-SDI. This is how many new products have a single port for both SDI and HDSDI.

The color space is differnet, REC601 for SDI and REC709 for HDSDI, but that's has no bearing on data transport.

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post #13 of 96 Old 07-20-2006, 10:44 AM
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Now we are getting somewhere, thanks Glimmie

Is hardware & not conception or HDCP the reason there are so many problems with DVI & HDMI interfaces?

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post #14 of 96 Old 07-20-2006, 11:18 AM
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Quote:
Originally Posted by Glimmie View Post

What are you saying is different assuming SMPTE292? Yes the ancillary data areas are a bit different but it's still 10bit Y and 10bit pBpR in a 4:2:2 cadence. Yes the clock rate is higher. HDSDI also uses the same NRZI scrambling algorithm as SDI. The electrical interface is also identical, 800mvpp across 75ohms. In fact they are so similar that modern chip sets do both SDI and HD-SDI. This is how many new products have a single port for both SDI and HDSDI.

The color space is differnet, REC601 for SDI and REC709 for HDSDI, but that's has no bearing on data transport.

Of course you're right, thanks for your comment.
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post #15 of 96 Old 07-20-2006, 11:32 AM
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What about HD-SDI vs SDI cable? Is it the same RG-6 cable? Are there any PQ different between good RG-6 cable?
Thanks
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post #16 of 96 Old 07-20-2006, 11:49 AM
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Quote:
Originally Posted by ex-airforce View Post

What about HD-SDI vs SDI cable? Is it the same RG-6 cable? Are there any PQ different between good RG-6 cable?
Thanks

It might perhaps depend on the length of the cable. But for any sane home cinema purpose there shouldn't be any differences. Somebody once told me I could use a wet clothesline for my SDI connection and that would work just fine, too!
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post #17 of 96 Old 07-20-2006, 11:56 AM
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SDI is set up for 75 ohm coaxial cable, whether SD or HD. This can be RG-6 (most common), RG-11 or RG 59.

PQ differences? For most people in most situations differences in cable quality will not be visible. Exceptions in home video would be for long distances, the very best equipment that would be capable of revealing any differences, or highly sensitive/trained/videophile oriented beholders.

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post #18 of 96 Old 07-20-2006, 11:57 AM
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... nevermind ...

- Emily (Litella)

Regards,

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post #19 of 96 Old 07-20-2006, 12:04 PM
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So....Pure silver 99.999 % 75 ohm RG-6 coaxial cable will give the same PQ as Belden 1694A RG-6 cable?
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post #20 of 96 Old 07-20-2006, 12:17 PM
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Yep, although I'd put it the other way around ...

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post #21 of 96 Old 07-20-2006, 02:30 PM
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Quick blurb I found about SMPTE 372M & why it is necessary.

"Dual Link HD-SDI 4:4:4 is the newest television standard using two HD-SDI video cables for twice the color resolution.

"Conventional SD and HD video is 4:2:2 based, which limits color detail to half the original image resolution. Dual Link 4:4:4 HD video preserves the full color detail - important for critical keying and feature film work."

I imagine the same extends to 424M

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post #22 of 96 Old 07-20-2006, 02:44 PM
 
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Note that in the home, video content is 4:2:0.
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post #23 of 96 Old 07-20-2006, 02:49 PM
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Quote:
Originally Posted by ChrisWiggles View Post

Note that in the home, video content is 4:2:0.

Correct but the SMPTE292 HDSDI still carries 4:2:2 framework. In the case of 4:2:0, the additional chroma space is just unsued.*

*But due to NRZI scrambling it's not just all zeros. The scrambling makes sure there are not long strings of zeros as this makes clock recovery very difficult. If course the perallel output from the deserializer would have all zeros in the unused chroma bit cells.

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post #24 of 96 Old 07-20-2006, 02:51 PM
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Quote:
Originally Posted by ex-airforce View Post

So....Pure silver 99.999 % 75 ohm RG-6 coaxial cable will give the same PQ as Belden 1694A RG-6 cable?

1694 is useful up to 300 feet, at least that's my design limit for the stuff. Longer than that we use Belden 7731 which is basically RG11. Nasty stuff. Has 14ga center conductor. Requires expensive BNC connectors and a strong hand to crimp them!.

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post #25 of 96 Old 07-20-2006, 02:51 PM
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CWiggles,
Does not necessarily have to be so.

What is really bringing about the change here is the affordability & proliferation of high end editing gear via PC's. This also assures that HD-SDI in its many forms is not going anywhere nor can the tap be turned off by anything other than chip design in terms of Consumer Gear. Wide open tap in the editing broadcast world.

One could easily enough assemble a Editing PC that could output 4:4:4 in HD-SDI.

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post #26 of 96 Old 07-20-2006, 02:59 PM
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I should note that there is a version of HD-SDI that has copy encryption built in. The concern is with digital cinema and the link between the server and projector. The studios don't think it's all that unlikely that a piracy group could acquire a professional HD VTR and simply record the stream from the server. It's upwards of 200mbs JPEG2000 so the quality is more than sufficient to make excellent bootleg HD-DVD's.

The key exchange is done through a CAT5 netwerk link to the projector from the server. My initial concerns with this was the NRZI scrambling would be broken by the encryption algorithm. This would make too long strings of ones and zeros which impede clock recovery. But they did a good job on that. So far it has proven very robuts in tests.

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post #27 of 96 Old 07-21-2006, 12:01 AM
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Glimmie,

surprising. Still, I would prefer encrypted HD-SDI over HDMI any day of the week.

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post #28 of 96 Old 07-21-2006, 06:15 AM
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Quote:
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Still, I would prefer encrypted HD-SDI over HDMI any day of the week.

Would you still prefer it even if they look the same?

Can encrypted HD-SDI be converted to analog for a CRT like HDMI can?
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post #29 of 96 Old 07-21-2006, 07:41 AM
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Quote:
Originally Posted by Erik Garci View Post

Would you still prefer it even if they look the same?

SDI cables are a lot cheaper and more robust than HDMI ones are.

Quote:


Can encrypted HD-SDI be converted to analog for a CRT like HDMI can?

If you unencrypt it...
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post #30 of 96 Old 07-21-2006, 02:08 PM
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Quote:
Originally Posted by ChrisWiggles View Post

Note that in the home, video content is 4:2:0.

I thought MPEG decoders upsampled to 4:2:2? Or did I miss something?

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